feat(windows): UIA cursor context; pace SendInput keystrokes

[DepengWang]

Summary

Brings Cursor Context to Windows. The feature already exists on macOS (via AX): it reads a small window of text around the host app's caret and passes it to LLM polish, which helps with homophones and domain terms. This PR adds the Windows half using UI Automation and reuses the existing HostContextAdapter -> cursor_context_input() pipeline, so there is no parallel path.

It also includes one unrelated Windows fix found while testing (dropped characters in SendInput insertion mode). It is a separate commit and can be split out if preferred.

Changes

Cursor context on Windows

• host_document/windows.rs: UIA reader. Prefers TextPattern2::GetCaretRange, falls back to TextPattern::GetSelection for collapsed selections only, and never guesses a caret from ValuePattern. The text window is built by expanding a range from the caret, so the whole document is never read; Core's existing window_around_cursor / plan_window then slices it to budget.
• Gated by the same password-field (CurrentIsPassword) and process-blocklist checks as the existing edit watcher, plus a focus-consistency recheck before returning, so an Alt+Tab mid-read cannot mix text from two apps.
• Runs on spawn_blocking with a 1s outer timeout. Any failure degrades to "no context" and dictation continues.
• Settings: the Cursor context toggle is now shown on Windows as well as macOS (still hidden on Linux, which has no implementation). All 8 locale descriptions and the types.ts doc comment drop the "macOS only" wording.
• Logging: the real dictation path now logs capture metadata (status, chars before/after, elapsed, app), matching what the debug probe already logged. No document text is ever logged.
• README.md / README.zh.md: document Windows support and the VS Code requirement below.

Unrelated fix: SendInput dropped characters (unicode_keystroke.rs, commit 50a02da2)

• With windowsInsertionMode=sendInput, mixed Chinese/English dictation lost the leading characters of a Latin word right after a CJK-to-ASCII transition ("open" arrived as "pen"). Characters inside a 16-char chunk were sent with no delay.
• Adds a 1ms gap after every character, mirroring the existing macOS INTER_KEYSTROKE_DELAY.

Testing

Verified on a real Windows 11 machine using Settings -> Experiments & Extensions -> cursor context probe:

• Notepad, Chrome <textarea>, VS Code: caret position correct, including with the caret in the middle of existing text.
• Password field on a real Chrome login page: Blocked/secure_text_field.
• Windows Terminal: Blocked/blocked_app.
• Captured context reaches the LLM polish prompt during a real dictation.
• SendInput fix: the dropped-character case no longer reproduces, with no noticeable typing delay.

Not tested:

• Word, Outlook, Edge, WeChat, WeCom, Teams, password managers.
• The UIA timeout path against a genuinely hung host app.
• macOS regression (no Mac available). The shared files touched are core_adapters.rs, host_document/mod.rs and openless-core/src/host_document/window.rs.

Known limitation

VS Code and other Chromium/Electron editors only keep the accessibility tree's caret in sync once they detect an accessibility client. With default settings the read succeeds but can return a stale position. Setting editor.accessibilitySupport to on and reloading the window fixes it. This is documented in both READMEs.

Screenshot

Windows, Settings -> Permissions & data. The Cursor context (experimental) toggle is now available on Windows. Taken from a local build that also has #1133 merged, which is why the encrypted sync card below shows a self-hosted token sign-in.

🤖 Generated with Claude Code