feat(tree): graphify tree — D3 v7 collapsible-tree HTML emitter

Adds a new `graphify tree` subcommand that emits a self-contained D3
v7 collapsible-tree HTML view of an existing graph.json.

Why
---
The existing `graph.html` (force-directed) is great for finding hubs
and unexpected connections.  But for code review and onboarding, a
hierarchical tree-of-modules view is much faster: you can collapse
everything and expand only the package you care about, the depth-
based colour palette gives instant orientation, and the layout
mirrors the on-disk structure.

The look + feel is a near-verbatim port of the TGI Taxonomy Viewer
(expand-all / collapse-all / reset-view buttons, multi-line
`wrapText` labels with separately-coloured name + count, depth-based
palette, click-to-toggle subtree, hover-inspector showing top-K
outbound edges per symbol).

Implementation
--------------
- `graphify/tree_html.py` (575 LOC, single file, no new runtime
  dependencies).  D3 v7 is loaded from cdn.jsdelivr.net at view time.
- Hierarchy is built from `source_file` longest-common-prefix;
  symbols are grouped by containing module so the tree mirrors the
  on-disk layout exactly.
- Inspector pre-computes top-K outbound edges per symbol so the page
  works fully offline once loaded.
- `__main__.py` adds the subcommand + help text after the
  `check-update` block.

Configuration
-------------
- `--graph PATH`     path to graph.json (default: graphify-out/graph.json)
- `--output HTML`    output path (default: graphify-out/GRAPH_TREE.html)
- `--root PATH`      filesystem root (default: LCP of source_files)
- `--max-children N` cap visible children per node (default: 200)
- `--top-k-edges N`  per-symbol outbound edges in inspector (default: 12)
- `--label NAME`     project label shown in the page header

Tested locally on a 17 641-node graph — emits a 4.9 MB HTML file
that renders smoothly in Firefox / Chromium.

Author: dsremo

CHANGELOG.md

@@ -2,6 +2,21 @@
 
 Full release notes with details on each version: [GitHub Releases](https://github.com/safishamsi/graphify/releases)
 
+## Unreleased — `graphify tree` subcommand
+
+- **New:** `graphify tree` — emits a self-contained D3 v7 collapsible-tree HTML
+  view of `graph.json`.  Same look + feel as the *TGI Taxonomy Viewer*: expand-
+  all / collapse-all / reset-view buttons; multi-line `wrapText` labels with
+  separately-coloured name + count; depth-based colour palette; click-to-
+  toggle subtree; hover inspector showing top-K outbound edges per symbol.
+- Hierarchy is built from `source_file` longest-common-prefix; symbols are
+  grouped by their containing module so the tree mirrors the on-disk layout.
+- Configuration: `--graph PATH`, `--output HTML`, `--root PATH`,
+  `--max-children N` (default 200), `--top-k-edges N` (default 12),
+  `--label NAME`.
+- Implementation: `graphify/tree_html.py` (575 LOC, no external runtime
+  dependencies — D3 v7 is loaded from cdn.jsdelivr.net).
+
 ## 0.4.23 (2026-04-18)
 
 - Fix: stale skill version warning persists after running `graphify install` when multiple platforms were previously installed — `graphify install` now refreshes `.graphify_version` in all other known skill directories so the warning clears across the board (#178)

graphify/__main__.py

@@ -1004,6 +1004,13 @@ def main() -> None:
         print("    --nodes N1 N2 ...       source node labels cited in the answer")
         print("    --memory-dir DIR        memory directory (default: graphify-out/memory)")
         print("  check-update <path>     check needs_update flag and notify if semantic re-extraction is pending (cron-safe)")
+        print("  tree                    emit a D3 v7 collapsible-tree HTML for graph.json")
+        print("    --graph PATH            path to graph.json (default graphify-out/graph.json)")
+        print("    --output HTML           output path (default graphify-out/GRAPH_TREE.html)")
+        print("    --root PATH             filesystem root for the hierarchy")
+        print("    --max-children N        cap children per node (default 200)")
+        print("    --top-k-edges N         per-symbol outbound edges in inspector (default 12)")
+        print("    --label NAME            project label in header")
         print("  benchmark [graph.json]  measure token reduction vs naive full-corpus approach")
         print("  hook install            install post-commit/post-checkout git hooks (all platforms)")
         print("  hook uninstall          remove git hooks")
@@ -1422,6 +1429,62 @@ def main() -> None:
         from graphify.watch import check_update
         check_update(Path(sys.argv[2]).resolve())
         sys.exit(0)
+    elif cmd == "tree":
+        # Emit a TGI-style D3 v7 collapsible tree HTML for an existing
+        # graph.json. Same look + feel as the TGI taxonomy viewer:
+        # expand-all / collapse-all / reset-view buttons, multi-line
+        # wrapText labels with separately-coloured name + count,
+        # depth-based palette, click-to-toggle subtree.
+        from typing import Optional as _Opt
+        from graphify.tree_html import write_tree_html, DEFAULT_MAX_CHILDREN
+        graph_path = Path("graphify-out/graph.json")
+        output_path: "_Opt[Path]" = None
+        root: "_Opt[str]" = None
+        max_children = DEFAULT_MAX_CHILDREN
+        top_k_edges = 0
+        project_label: "_Opt[str]" = None
+        args = sys.argv[2:]
+        i_arg = 0
+        while i_arg < len(args):
+            a = args[i_arg]
+            if a == "--graph" and i_arg + 1 < len(args):
+                graph_path = Path(args[i_arg + 1]); i_arg += 2
+            elif a == "--output" and i_arg + 1 < len(args):
+                output_path = Path(args[i_arg + 1]); i_arg += 2
+            elif a == "--root" and i_arg + 1 < len(args):
+                root = args[i_arg + 1]; i_arg += 2
+            elif a == "--max-children" and i_arg + 1 < len(args):
+                max_children = int(args[i_arg + 1]); i_arg += 2
+            elif a == "--top-k-edges" and i_arg + 1 < len(args):
+                top_k_edges = int(args[i_arg + 1]); i_arg += 2
+            elif a == "--label" and i_arg + 1 < len(args):
+                project_label = args[i_arg + 1]; i_arg += 2
+            elif a in ("-h", "--help"):
+                print("Usage: graphify tree [--graph PATH] [--output HTML]")
+                print("  --graph PATH         path to graph.json (default graphify-out/graph.json)")
+                print("  --output HTML        output path (default graphify-out/GRAPH_TREE.html)")
+                print("  --root PATH          filesystem root (default: longest common dir of all source_files)")
+                print("  --max-children N     cap visible children per node (default 200)")
+                print("  --top-k-edges N      pre-compute top-K outbound edges per symbol (default 12)")
+                print("  --label NAME         project label shown in the page header")
+                return
+            else:
+                i_arg += 1
+        if not graph_path.is_file():
+            print(f"error: graph.json not found at {graph_path}", file=sys.stderr)
+            sys.exit(1)
+        if output_path is None:
+            output_path = graph_path.parent / "GRAPH_TREE.html"
+        out = write_tree_html(
+            graph_path=graph_path, output_path=output_path,
+            root=root, max_children=max_children,
+            top_k_edges=top_k_edges, project_label=project_label,
+        )
+        size_kb = out.stat().st_size / 1024
+        print(f"wrote {out} ({size_kb:.1f} KB)")
+        print(f"open with: xdg-open {out}  (or file://{out.resolve()})")
+        sys.exit(0)
+
     elif cmd == "merge-graphs":
         # graphify merge-graphs graph1.json graph2.json ... --out merged.json
         args = sys.argv[2:]