feat(ms-ai-architect): replace playground v2 with v3 + docs update

Step 17 (Wave 5, final). Closes the v3 playground delivery (5-session run,
17 commits total).

Pre-flight tests verified passing before deletion:
- bash tests/validate-plugin.sh -> 215/215 PASS
- bash tests/run-e2e.sh --playground -> 240/240 PASS (170 + 70)

Changes:
- DELETE playground/ms-ai-architect-v3.html
- MOVE v3 content to playground/ms-ai-architect-playground.html (3867 lines).
  Replaces the deleted v2 file at the same canonical path so external
  references continue to resolve.
- UPDATE tests/test-playground-v3.sh + tests/test-playground-parsers.sh
  to point at the renamed canonical file.
- UPDATE plugin README.md (## Playground (v3) section): describes the
  4-surface decision-builder + report-viewer architecture, persistent state
  model, 17 report renderers, theme toggle, and the validation matrix.
- UPDATE plugin CLAUDE.md: replaces v2 5-step pipeline section with v3
  architecture overview. Marks docs/playground-v2-spec.md as historical-only
  (no longer the contract); points at .claude/projects/2026-05-03-playground
  -v3-architecture/ for v3 spec.
- UPDATE root README.md: marketplace listing for ms-ai-architect now
  describes v3 architecture (4 surfaces, persistence, 17 renderers, theme,
  240-test validation) and references the test command.

Verify (post-rename):
- ! test -f playground/ms-ai-architect-v3.html: pass
- test -f playground/ms-ai-architect-playground.html (>3000 lines): pass
- grep -q "v3" in plugin README + plugin CLAUDE.md + root README: pass
- bash tests/validate-plugin.sh: exit 0 (215/215)
- bash tests/run-e2e.sh --playground: exit 0 (240/240)

plugins/ms-ai-architect/README.md

@@ -348,14 +348,30 @@ Two runtime hooks provide session context and safety guardrails:
 
 ---
 
-## Playground
+## Playground (v3)
 
-Interactive 5-step architecture pipeline for Microsoft AI decisions, runnable from `file://` without a server.
+Interactive **decision-builder + report viewer** for Microsoft AI architecture decisions, runnable from `file://` without a server. Replaces the v2 5-step pipeline with a multi-surface app that persists state across sessions and visualizes parsed reports inline.
 
-- **File:** `playground/ms-ai-architect-playground.html`
-- **Pipeline:** Intake (wizard) → Explore (filtered catalog) → Configure (parameters + compliance) → Review (cost P10/P50/P90 + risk) → Export (4 formats)
-- **3 entry modes:** "Guide me" (wizard), "Let me explore" (browse), "I know what I want" (direct)
-- **4 export formats:** Structured prompt, command pipeline (per-command copy), Markdown brief, JSON Decision Record
+- **File:** `playground/ms-ai-architect-playground.html` (~3870 lines, single-file v3 architecture)
+- **4 surfaces:** Onboarding (18 shared fields) → Home (project list + 3 entry tracks) → Catalog (24 commands grouped by 5 expansion categories with search) → Project (per-project tabs, command form prefill, paste-back report import + visualization)
+- **Persistent state:** IndexedDB primary store with localStorage fallback. Schema-versioned (`STATE_KEY = 'ms-ai-architect-state-v1'`) with eager `MIGRATIONS` pipeline.
+- **17 report renderers:** Each report-producing command has a parser (markdown → structured) and renderer (structured → HTML visualization: pyramid, matrix, radar, findings, distribution, capability-matrix, etc.) wired through a canonical archetype-routing table.
+- **Theme:** Dark default + light mode toggle, persisted in `localStorage('ms-ai-architect-theme')`.
+- **Export/import:** JSON Decision Record envelope (Blob + FileReader), schema-version-aware on import.
+
+```bash
+# Run playground locally
+open plugins/ms-ai-architect/playground/ms-ai-architect-playground.html
+```
+
+### Validation
+
+| Test | Command | Coverage |
+|------|---------|----------|
+| Static structure | `bash tests/test-playground-v3.sh` | 170 PASS — vendored CSS, surfaces, 24 commands, 14 parsers, 17 renderers, design-system classes, action handlers |
+| Parser fixtures | `bash tests/test-playground-parsers.sh` | 70 PASS — 17 fixtures × parser routing |
+| Combined (E2E) | `bash tests/run-e2e.sh --playground` | both above |
+| Manual a11y QA | See `playground/MANUAL-CHECKLIST.md` | 10 sections incl. axe-core run per surface |
 
 ### Vendored design-system
 
@@ -365,11 +381,6 @@ The playground loads CSS from `playground/vendor/playground-design-system/` —
 - **Drift detection:** `MANIFEST.json` records SHA-256 per file. Re-sync refuses to overwrite files modified locally — pass `--force` to override.
 - **Generated header:** Each vendored CSS file is prefixed with `/* Code generated by sync-design-system.mjs; DO NOT EDIT. */`. Edit `shared/`, then re-sync.
 
-```bash
-# Run playground locally
-open plugins/ms-ai-architect/playground/ms-ai-architect-playground.html
-```
-
 ---
 
 ## Technology Coverage