Epic: UI/UX & docs polish

[ApocDev]

Cross-cutting polish on the web app's look, responsiveness, and documentation, distinct from the 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 (images, worked examples, deeper coverage).
• Holistic UX/UI design pass across the web app #17 — holistic UX/UI design pass across the web app.
• Polish release notes with AI (nicer GitHub release body + in-app update dialog) #54 — polish release notes with AI (nicer GitHub release body + in-app update dialog).
• Handle query/route errors: error states, boundaries, consistent loading #81 — query/route error states, boundaries, consistent loading.
• Export/import: project backup and shareable block/plan JSON #82 — export/import: project backup and shareable block/plan JSON.
• Consistent destructive actions: one confirm pattern, undo toast, delete non-empty blocks #83 — consistent destructive actions (confirm pattern, undo toast, delete non-empty blocks).
• Project switcher: real create dialog and soft navigation #84 — project switcher: real create dialog and soft navigation.
• Modal hygiene: Escape, focus trap, and dialog semantics on hand-rolled pickers #86 — modal hygiene: Escape, focus trap, dialog semantics on hand-rolled pickers.
• Shared filtered-list primitive (six pages hand-roll search) #87 — shared filtered-list primitive.
• Warn when DB migrations are pending (restart needed) #75 — warn when DB migrations are pending (restart needed).
• Factory view: sortable columns, %-met severity, collapsible sections (late-game scale) #77 — factory view: sortable columns, %-met severity, collapsible sections.
• Command palette: Ctrl+K / / search-everything #78 — command palette: Ctrl+K / / search-everything.
• Undo system: trigger-based undo log with multi-level Ctrl+Z #90 — undo system: trigger-based undo log with multi-level Ctrl+Z.