Epic: UI/UX & docs polish

[ApocDev]

Cross-cutting polish on the web app look, responsiveness, and documentation, distinct from feature work that adds new surfaces.

Sub-issues:

• Responsive/mobile: make the app usable on small screens #9 — responsive and small-screen usability.
• Flesh out the in-app help drawers (images, worked examples, deeper coverage) #16 — flesh out the in-app help drawers.
• Holistic UX/UI design pass across the web app #17 — holistic UX/UI design pass.
• Polish release notes with AI (nicer GitHub release body + in-app update dialog) #54 — polish release notes with AI.
• Warn when DB migrations are pending (restart needed) #75 — warn when DB migrations are pending.
• Factory view: sortable columns, %-met severity, collapsible sections (late-game scale) #77 — improve late-game Factory view scaling.
• Command palette: Ctrl+K / / search-everything #78 — command palette.
• Handle query/route errors: error states, boundaries, consistent loading #81 — consistent query, route, loading, and error states.
• Export/import: project backup and shareable block/plan JSON #82 — project backup and shareable plan import/export.
• Consistent destructive actions: one confirm pattern, undo toast, delete non-empty blocks #83 — consistent destructive actions and undo.
• Project switcher: real create dialog and soft navigation #84 — project create/switch flow.
• Modal hygiene: Escape, focus trap, and dialog semantics on hand-rolled pickers #86 — modal accessibility and semantics.
• Shared filtered-list primitive (six pages hand-roll search) #87 — shared filtered-list primitive.
• Undo system: trigger-based undo log with multi-level Ctrl+Z #90 — multi-level undo system.
• Build hosted end-user and developer documentation site #141 — hosted user and developer documentation.
• Harden light and dark theme contrast #107 — harden light/dark semantic contrast and add automated theme QA.

All earlier children are complete. Close this epic after #107 lands.