chore: complete v1.1 milestone — Fixes & Polish

Archive v1.1 artifacts (roadmap, requirements, phases) to milestones/.
Evolve PROJECT.md with shipped requirements and new key decisions.
Reorganize ROADMAP.md with collapsed milestone groupings.
Update retrospective with v1.1 lessons.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.planning/MILESTONES.md

@@ -1,5 +1,23 @@
 # Milestones
 
+## v1.1 Fixes & Polish (Shipped: 2026-03-15)
+
+**Phases completed:** 3 phases, 7 plans
+**Timeline:** 1 day (2026-03-15)
+**Codebase:** 6,134 LOC TypeScript, 65 files changed (+5,049 / -1,109)
+
+**Key accomplishments:**
+- Fixed threads table and thread creation with categoryId support, modal dialog flow
+- Overhauled planning tab with educational empty state, pill tabs, and category filter
+- Fixed image display bug (Zod schemas missing imageFilename — silently stripped by validator)
+- Redesigned image upload as hero preview area with 4:3 placeholders on all cards
+- Migrated categories from emoji to Lucide icons with 119-icon curated picker
+- Built IconPicker component with search, 8 group tabs, portal popover
+
+**Archive:** `.planning/milestones/v1.1-ROADMAP.md`, `.planning/milestones/v1.1-REQUIREMENTS.md`
+
+---
+
 ## v1.0 MVP (Shipped: 2026-03-15)
 
 **Phases completed:** 3 phases, 10 plans