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/STATE.md

@@ -3,14 +3,14 @@ gsd_state_version: 1.0
 milestone: v1.1
 milestone_name: Usability and Templates
 status: planning
-stopped_at: Phase 5 context gathered
-last_updated: "2026-03-12T10:54:48.549Z"
+stopped_at: Completed 05-template-data-model-and-api-01-PLAN.md
+last_updated: "2026-03-12T11:07:58.758Z"
 last_activity: 2026-03-12 — v1.1 roadmap created, Phases 5-8 defined
 progress:
   total_phases: 8
   completed_phases: 4
-  total_plans: 10
-  completed_plans: 10
+  total_plans: 12
+  completed_plans: 11
   percent: 0
 ---
 
@@ -50,6 +50,7 @@ Progress: [░░░░░░░░░░] 0%
 - Trend: -
 
 *Updated after each plan completion*
+| Phase 05-template-data-model-and-api P01 | 3 | 2 tasks | 4 files |
 
 ## Accumulated Context
 
@@ -63,6 +64,9 @@ Recent decisions affecting current work:
 - [Phase 03]: triggerFlash uses two separate state vars (flashRowId/errorRowId) — no race conditions between success and error states
 - [Phase 03]: EmptyState is a shared component with all content as props — icon, heading, subtext, and optional CTA
 - [Init v1.1]: Three-tier item model (fixed/variable/one-off) matches how users think about recurring vs one-time expenses
+- [Phase 05-template-data-model-and-api]: New API-created budget items default to item_tier=one_off at the query layer
+- [Phase 05-template-data-model-and-api]: Template creation is lazy: CreateTemplateItem upserts template via ON CONFLICT
+- [Phase 05-template-data-model-and-api]: GenerateBudgetFromTemplate returns BudgetExistsError struct for structured 409 response
 
 ### Pending Todos
 
@@ -75,6 +79,6 @@ None yet.
 
 ## Session Continuity
 
-Last session: 2026-03-12T10:54:48.547Z
-Stopped at: Phase 5 context gathered
-Resume file: .planning/phases/05-template-data-model-and-api/05-CONTEXT.md
+Last session: 2026-03-12T11:07:58.757Z
+Stopped at: Completed 05-template-data-model-and-api-01-PLAN.md
+Resume file: None