feat: add surface-aware shortcuts

[BorisTyshkevich]

Summary

Adds a shared, surface-aware shortcut catalog for SQL Browser and Dashboard.

• Renders contextual, platform-aware, accessible shortcut help with focus management and a scroll-safe modal.
• Adds Dashboard refresh, View/Edit, and G navigation commands while preserving Workbench commands on SQL Browser only.
• Registers refresh against the current Dashboard viewer generation and clears it during surface transitions, preventing stale-session dispatch.
• Uses tokenized keyboard ownership for dialogs, stacked result drawers, menus/popovers, and detached fallback overlays so application shortcuts cannot execute behind them.
• Tears down contextual shortcut help across navigation, popstate, sign-out, authentication loss, and workspace error surfaces.
• Dispatches navigation chords from the same executable catalog used by help, including nested role="textbox" suppression.

Why

The shared shortcut-help control previously documented Workbench commands on Dashboard and ? could not open contextual help there.

Review also identified modal surfaces that did not participate in keyboard ownership, stale body-mounted help surviving surface/authentication transitions, and a separately hardcoded chord routing table. Those gaps could run commands behind dialogs, cancel a query with the same Escape used to close a result drawer, and let help drift from runtime behavior.

Validation

• npm test — 5,083 passing tests; strict TypeScript, architecture checks, and per-file coverage gates pass.
• npm run build — single-file dist/sql.html build succeeds.

Closes #417.