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>

tools/gitea.ts

@@ -104,7 +104,7 @@ async function main() {
             }
           }
         } else if (sub === 'create') {
-          const [,, head, base, title, ...bodyParts] = args;
+          const [, head, base, title, ...bodyParts] = args;
           const body = bodyParts.join(' ') || '';
           if (!head || !base || !title) {
             console.error('Usage: bun tools/gitea.ts prs create <head_branch> <base_branch> <title> [body]');