Add pure-Python view API as alternative to cgx templates

[berendkleinhaneveld]

What

Adds a pure-Python way to describe component UIs — the view() method — as a fully supported alternative to .cgx templates, for users who prefer to stay in plain Python (better tooling, type checkers, no separate file format):

import collagraph as cg
from collagraph import h


class Counter(cg.Component):
    def init(self):
        self.state["count"] = 0

    def bump(self):
        self.state["count"] += 1

    def view(self):
        with h.widget():
            h.label(lambda: f"Count: {self.state['count']}")
            h.button("bump", on_clicked=self.bump)

Templates remain fully supported; the two coexist (a component defines either a template or a view method).

How it works

Like compiled cgx render functions, view() runs once per component instance: it's a setup function that builds the same Fragment tree the compiler produces, so all fine-grained reactivity lives in the existing Fragment layer — no new reactivity machinery. The one rule: a plain value is a static attribute, a zero-arg callable is a reactive bind.

The full template feature set is covered: static/bound attributes and bind= dicts, events (on_*), text content, when/elif_/otherwise, keyed and unkeyed each loops (loop variables as Solid-style getters), component usage with props/events, slots and fill, refs, and dynamic (:is) components. View build code additionally runs inside a temporary watcher that detects the eager-read footgun (reading reactive state without wrapping it in a lambda) and warns with a pointer to the fix.

Also in this PR

• Hot reload for view components: plain .py modules defining view components are watched and reloaded, including scripts run directly (python my_app.py — the file is re-executed under a substitute module name so the __main__ guard doesn't re-fire). Also fixes a stale-bytecode edge where a same-size rewrite within the same mtime second would reload old code.
• CLI support: collagraph -H examples/pyside/counter_view.py works, with file.py:ClassName to select a class when a module defines several.
• Examples (counter_view.py, todo_view.py), a docs guide (Python Views, with a template→Python cheat sheet), and cross-links from the existing docs.
• Drive-by fix: <window title=...> in the todo example was a silent no-op (the Qt property is windowTitle); now uses window_title.

Testing

• 33 new tests (view DSL, hot reload of view modules, CLI resolution); full suite passes.
• Examples verified end-to-end against an offscreen QApplication, including keyed list reconciliation and conditional switching.
• Hot reload verified end-to-end offscreen with the watchdog enabled: edit on disk → reload → state preserved → UI still interactive, both programmatically and through collagraph -H.
• mkdocs build --strict passes.

🤖 Generated with Claude Code