fix: restore WASM static file serving configuration

Reverted breaking changes from commit 08b002d (2026-07-04 20:28):

1. UseStaticFiles path mapping (reverted):
   - Before (c960860 - working): app.UseStaticFiles("/admin")
   - After (08b002d): app.UseStaticFiles(new StaticFileOptions { RequestPath = "/admin" })
   - Now (fixed): app.UseStaticFiles("/admin") ✅

2. Removed MapRazorComponents (blocking WASM):
   - app.MapRazorComponents<...>() was interfering with static file serving
   - Blazor WebAssembly should be pure static WASM, not server-side
   - Removed in favor of MapFallbackToFile pattern ✅

3. Restored portal fallback:
   - Added app.MapFallbackToFile("portal/{*path:nonfile}", "portal/index.html")
   - Added root redirect: app.MapGet("/", ...)

4. Fixed index.html script path:
   - Before: <script src="/_framework/blazor.webassembly.js"></script> (absolute)
   - After: <script src="_framework/blazor.webassembly.js"></script> (relative)
   - Relative path respects base href="/taxbaik/admin/" ✅

**Verification:**
- WASM files (45KB+): ✅ Present, correct hash
- Server delivery: ✅ 200 OK, correct SHA-256
- Static file serving: ✅ /taxbaik/admin/_framework/* accessible
- Issue: blazor.boot.json still missing (blocks WASM initialization)

**Status:**
- Login form: ✅ Renders
- WASM bootstrap script: ✅ Loads (with relative path fix)
- WASM runtime: ❌ Blocked (needs blazor.boot.json)
- Dashboard: ❌ Loading indefinitely

Next: Investigate why blazor.boot.json is not generated in Debug build.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/TaxBaik.Web/wwwroot/admin/index.html

@@ -18,6 +18,6 @@
         <a class="dismiss">🗙</a>
     </div>
 
-    <script src="/_framework/blazor.webassembly.js"></script>
+    <script src="_framework/blazor.webassembly.js"></script>
 </body>
 </html>