feat: add Windows native dialog automation

[Hushlor]

Summary

• add Windows-only native_dialog_snapshot and native_dialog_interact MCP tools backed by Microsoft UI Automation on a dedicated COM MTA thread
• support message and confirmation dialogs, single- and multi-file Open, Save, folder selection, overwrite confirmation, and advertised navigation controls
• follow bounded same-process dialog ownership chains while keeping opaque references session-scoped and short-lived
• add Windows E2E coverage, unit tests, test-app fixtures, API documentation, and changelog entries

Security and scope

• only visible dialogs in the connected Tauri process whose owner chain leads to the targeted Tauri window are exposed
• interaction revalidates the process, owner chain, window visibility, session scope, element process, and advertised UI Automation pattern
• path values are validated without being logged or echoed in interaction results
• non-Windows platforms return a clear unsupported-platform error

Validation

• npm run standards
• npm run test:unit -w @hypothesi/tauri-mcp-server — 65 passed
• npm run test:e2e -w @hypothesi/tauri-mcp-server — 162 passed, 1 skipped
• native Windows dialog E2E — all 9 scenarios passed against real dialogs
• cargo test --manifest-path packages/tauri-plugin-mcp-bridge/Cargo.toml
• cargo clippy --manifest-path packages/tauri-plugin-mcp-bridge/Cargo.toml --all-targets -- -D warnings
• npm run docs:build

Closes #5