feat: refine quick actions and directory navigation

[willchen96]

Summary

• Reworks Quick Actions into named, editable shortcuts for Assistant workflows only. Adds create, update, delete, default installation, concise default prompts, and a Features setting that can hide the Quick Actions bar.
• Adds the database migration and fresh-install schema for Quick Action names and visibility preferences, removes legacy non-Assistant actions, and keeps default workflows and actions independently editable.
• Standardises Library, Project, workflow add-on, frontend document picker, and Word add-in directory behaviour: nested folder routes and breadcrumbs, inline expansion, folder selection, empty-folder states, updated-first ordering, metadata, and lazy loading in pages of 40.
• Adds folder URLs for Library and Projects, pack-folder views for workflow add-ons, query-backed tabs where appropriate, and responsive breadcrumb collapsing that keeps the current folder visible.
• Improves assistant interactions with earlier streamed chat titles, Reading and Read activity labels, clickable document events, stable side-panel document identity, file icons, and refined composer controls.
• Moves account sign-out into the account menu, adds the Quick Actions feature preference, avoids recent-project refresh flashes, and aligns table, toolbar, placeholder, spacing, and row typography across the application.
• Consolidates frontend and Word add-in SVG assets under shared/icons, adds settings, sign-out, legislation, and case-law artwork, and introduces build-time delivery for both applications.
• Updates the Word Add Documents experience to match the frontend directory model, including Files, Templates, and Projects, nested folders, cascading folder selection, uploads, and pagination.

Database

• Adds 20260814_02_assistant_quick_actions.sql.
• Adds quick_actions.name and user_profiles.quick_actions_visible.
• Backfills existing action names from workflow titles and removes actions linked to non-Assistant workflows.
• Updates default installation so only Assistant workflows receive Quick Actions.

Validation

• Backend: 608 tests passed; TypeScript build passed.
• Local Supabase stack: 15 integration tests passed.
• Frontend: 311 tests passed with 100% line and function coverage; lint passed with zero errors; production build passed.
• Word add-in: application and E2E typechecks passed; production webpack and manifest build passed.
• Word add-in Playwright: 222 unaffected scenarios passed; the six pagination URL mock failures found in Chromium and WebKit were corrected and all six targeted reruns passed.
• All shared SVGs pass XML validation and the generated frontend icon mirror matches the shared source.