feat(vault-tui): M5 slice 1 — read-only three-pane browser

Turn the vault-tui stub into a real cruxpass-style TUI (ratatui + crossterm):
left folder list, center filterable item list, right item detail, status bar.
It is just another UDS client of the agent — the user key never crosses into
it — and drives only the existing Request::Status + Request::List, so there is
no IPC change.

- Requires a pre-unlocked agent; locked/absent agent shows a centered banner.
  r refreshes (Status + List). Keys: q/Esc/Ctrl+C quit, j/k + arrows move,
  Tab/h/l switch pane focus. Folder selection (All/Unfiled/named, derived from
  entries) filters the item list. The status bar previews / c u o g : as
  coming-soon so the layout is final.
- Detail is read-only and secret-free this slice: only the non-secret
  ListEntry metadata (name/type/username/folder/id) the agent already returned.
  Reveal/copy (which need Request::Get) land with the copy slice.
- Terminal teardown is RAII + a panic hook, so a panic never leaves the
  terminal in raw mode. Input is read on a dedicated OS thread and forwarded
  over a tokio mpsc channel the loop awaits (no busy-poll). vault-tui --version
  carries the §13.2 attribution block.

New modules: app (state + pure nav/filter logic, 6 unit tests), ui (rendering
+ #RRGGBB->Color helper over vault_theme::steelbore, 2 TestBackend smoke
tests), client (UDS request helper).

deny.toml ignores RUSTSEC-2024-0436 (paste unmaintained) — a build-time-only
proc-macro with no runtime surface, pulled in transitively by ratatui.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: UnbreakableMJ

CHANGELOG.md

@@ -10,6 +10,30 @@ range may break in any release.
 
 ### Added
 
+- **M5 (slice 1) — `vault-tui` skeleton (read-only browser).** The TUI stub is
+  now a real cruxpass-style three-pane interface (`ratatui` + `crossterm`):
+  **left** folder list, **center** filterable item list, **right** item detail,
+  with a status bar. It is just another UDS client of the agent — the user key
+  never crosses into it — and drives only the existing `Request::Status` +
+  `Request::List`, so no IPC change.
+  - Requires a pre-unlocked agent; a locked or absent agent shows a centered
+    banner (`Locked` / `No agent`). `r` refreshes (re-runs Status + List).
+  - Keys: `q`/`Esc`/`Ctrl+C` quit, `j`/`k` + arrows move, `Tab`/`h`/`l` switch
+    pane focus. Folder selection filters the item list (`All` / `Unfiled` /
+    named folders, derived from the entries). The status bar previews the
+    `/ c u o g :` keys as coming-soon so the layout is final.
+  - Detail is **read-only and secret-free** this slice: it shows only the
+    non-secret `ListEntry` metadata (name, type, username, folder, id) the agent
+    already returned — reveal/copy (which need `Request::Get`) land with the copy
+    slice. Terminal teardown is RAII + a panic hook, so a panic never leaves the
+    terminal in raw mode. `vault-tui --version` carries the §13.2 block.
+  - New modules `app` (state + pure nav/filter logic, 6 unit tests), `ui`
+    (rendering + a `#RRGGBB`→`Color` theme helper over `vault_theme::steelbore`,
+    2 `TestBackend` render smoke tests), and `client` (UDS request helper).
+  - `deny.toml` ignores **RUSTSEC-2024-0436** (`paste` unmaintained) — a
+    build-time-only proc-macro with no runtime surface, pulled in transitively
+    by `ratatui`; documented with a revisit note.
+
 - **M4 (slice 4) — `--json` on the lifecycle verbs + a real `vault sync`.**
   Closes the two remaining M4 items.
   - `unlock`, `lock`, `sync`, and `stop-agent` now take `--json`. They stay