docs: modernize platform capability and architecture guides to DBK Platform (#5)

Fixes #1

### Summary of Changes
- Modernized architecture documents to establish DBK Platform as the canonical multi-tenant commerce platform identity, treating HomAroma as the reference tenant.
- Updated frontend comparison to accurately reflect apps/spa (React 19 + Vite) vs apps/website (Next.js 15 SSR) instead of legacy names.
- Cleaned typos in PRISMA7_GUIDE and added cross-references to docs/PLATFORM_OVERVIEW.md.
- Updated docs/DOCUMENTATION_MIGRATION.md completion tracking.

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Co-authored-by: Your Name <you@example.com>
Reviewed-on: #5
Co-authored-by: antigravity-bot <bot@kittisak.com>

docs/DOCUMENTATION_MIGRATION.md

@@ -13,6 +13,15 @@ See [Platform Overview](PLATFORM_OVERVIEW.md) for terminology.
 - `PROJECT_SYSTEM_SUMMARY.md`
 - `PROJECT_MANAGEMENT_PERSPECTIVE.md`
 - `LLM_MCP_GUIDE.md`
+- `ARCHITECTURE_DECISIONS.md`
+- `CUSTOM_BLOCK_FLOW_GUIDE.md`
+- `ADMIN_MCP_SECTION_GUIDE.md`
+- `PRISMA7_GUIDE.md`
+- `mcp_update.md`
+- `implementation_plan.md`
+- `frontend-comparison.md`
+- `BUSINESS_ANALYTICS_MAPS_PLAN.md`
+- `goal.section.md`
 
 These documents now introduce DBK Platform before mentioning HomAroma and explain
 the platform/tenant boundary.