docs(12-01): complete comparison view plan

- ComparisonTable component with 10 attribute rows and sticky label column
- Delta highlighting: blue-50 lightest weight, green-50 cheapest price, gray delta text
- Compare toggle in thread detail toolbar (visible for 2+ candidates)
- All COMP-01 through COMP-04 requirements marked complete

.planning/ROADMAP.md

@@ -42,7 +42,7 @@
 
 - [x] **Phase 10: Schema Foundation + Pros/Cons Fields** — Migrate schema and deliver pros/cons annotation UI (completed 2026-03-16)
 - [x] **Phase 11: Candidate Ranking** — Drag-to-reorder priority ranking with rank badges (completed 2026-03-16)
-- [ ] **Phase 12: Comparison View** — Side-by-side tabular comparison with relative deltas
+- [x] **Phase 12: Comparison View** — Side-by-side tabular comparison with relative deltas (completed 2026-03-17)
 - [ ] **Phase 13: Setup Impact Preview** — Per-candidate weight and cost delta against a selected setup
 
 ## Phase Details
@@ -83,7 +83,7 @@ Plans:
   2. The lightest candidate column is highlighted and all other columns show their weight difference relative to it; the cheapest candidate is highlighted similarly for price
   3. The comparison table scrolls horizontally on a narrow viewport without breaking layout; the attribute label column stays fixed on the left
   4. A resolved thread shows the comparison table in read-only mode with the winning candidate visually marked
-**Plans:** 1 plan
+**Plans:** 1/1 plans complete
 Plans:
 - [ ] 12-01-PLAN.md — ComparisonTable component + compare toggle wiring in thread detail
 
@@ -113,5 +113,5 @@ Plans:
 | 9. Weight Classification and Visualization | v1.2 | 2/2 | Complete | 2026-03-16 |
 | 10. Schema Foundation + Pros/Cons Fields | v1.3 | 1/1 | Complete | 2026-03-16 |
 | 11. Candidate Ranking | 2/2 | Complete    | 2026-03-16 | - |
-| 12. Comparison View | v1.3 | 0/1 | Not started | - |
+| 12. Comparison View | 1/1 | Complete   | 2026-03-17 | - |
 | 13. Setup Impact Preview | v1.3 | 0/TBD | Not started | - |