docs(05-01): complete template data model and API plan

- Create 05-01-SUMMARY.md documenting migration, models, and query functions
- Update STATE.md with decisions, metrics, and progress bar (92%)
- Update ROADMAP.md phase 5 progress (1/2 plans complete)
- Mark requirements TMPL-01, TMPL-02, TMPL-04 complete in REQUIREMENTS.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.planning/ROADMAP.md

@@ -91,7 +91,7 @@ Plans:
   2. A user's template can be created and fetched via the API — it contains fixed items (with amounts) and variable items (category only, no amount)
   3. One-off items are excluded from template contents — the API never includes them in template responses
   4. The template API endpoints are documented and return correct data for all three item tiers
-**Plans:** 2 plans
+**Plans:** 1/2 plans executed
 
 Plans:
 - [ ] 05-01-PLAN.md — DB migration (item_tier enum, templates/template_items tables) + Go models + query functions
@@ -153,7 +153,7 @@ Phases execute in numeric order: 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7 -> 8
 | 2. Layout and Brand Identity | v1.0 | 2/2 | Complete | 2026-03-12 |
 | 3. Interaction Quality and Completeness | v1.0 | 4/4 | Complete | 2026-03-12 |
 | 4. Chart Polish and Bug Fixes | v1.0 | 2/2 | Complete | 2026-03-12 |
-| 5. Template Data Model and API | v1.1 | 0/2 | Planning | - |
+| 5. Template Data Model and API | 1/2 | In Progress|  | - |
 | 6. Template Frontend and Workflow Replacement | v1.1 | 0/3 | Not started | - |
 | 7. Quick-Add Library | v1.1 | 0/2 | Not started | - |
 | 8. Layout and Density Rethink | v1.1 | 0/2 | Not started | - |