Validate and fix all documentation code examples; add OAuth2 auth events reference

[Copilot]

Every Python code example in the docs was audited for syntactic validity and API correctness. Several examples referenced non-existent methods, had syntax errors, or were missing entirely for new features.

Documentation fixes

• components/index.md: Select(..., ...) — positional ... after keyword args is a SyntaxError. Fixed to options=[...].
• window-management.md: Adopted upstream restructuring (handle = WindowProxy in native mode); fixed executable code blocks — handle.eval() → handle.proxy.eval(), handle.eval_with_result() → handle.proxy.eval_with_result().
• why-pywry.md: **0Auth2"** (number zero, mismatched quote) → **OAuth2**.

New content synced from main

• guides/multi-widget.md — composing Plotly, AG Grid, Div, and Toolbar in one window
• guides/oauth2.md — full OAuth2 guide (native + deploy modes)
• reference/auth*.md — 8 OAuth2 API reference pages
• mkdocs.yml — nav entries for all new pages
• pywry/auth/ module, frontend/src/auth-helpers.js, examples, and all associated tests brought in from the merged oauth2 PR

Auth events documentation (reference/events.md)

Five auth:* events used in auth-helpers.js and the OAuth2 backend were entirely absent from the event reference:

Event	Direction	Trigger
auth:login-request	JS → Python	window.pywry.auth.login()
auth:logout-request	JS → Python	window.pywry.auth.logout()
auth:state-changed	Python → JS	Login / session expiry
auth:token-refresh	Python → JS	Background token refresh
auth:logout	Python → JS	Server-side logout complete

Added auth:* to reserved namespaces, full directional event tables with payload shapes, and a window.pywry.auth JS API reference.

Flaky E2E test fixes

test_set_always_on_top and test_pywry_toast_is_available both fail intermittently on Windows CI when the WebView2 subprocess fails to register Chrome_WidgetWin_0 in time. Applied @retry_on_subprocess_failure(max_attempts=3, delay=1.0) — the same pattern already used across test_alerts.py — with runtime.stop() cleanup between attempts.

Final state: 317 Python code blocks across 50 documentation files — all syntactically valid.

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