feat: Implement Phase 4 Web Interface with bugfixes (v0.5.2)

## Phase 4: Web Interface Implementation

Implemented complete web interface with public and admin routes,
templates, CSS, and development authentication.

### Core Features

**Public Routes**:
- Homepage with recent published notes
- Note permalinks with microformats2
- Server-side rendering (Jinja2)

**Admin Routes**:
- Login via IndieLogin
- Dashboard with note management
- Create, edit, delete notes
- Protected with @require_auth decorator

**Development Authentication**:
- Dev login bypass for local testing (DEV_MODE only)
- Security safeguards per ADR-011
- Returns 404 when disabled

**Templates & Frontend**:
- Base layouts (public + admin)
- 8 HTML templates with microformats2
- Custom responsive CSS (114 lines)
- Error pages (404, 500)

### Bugfixes (v0.5.1 → v0.5.2)

1. **Cookie collision fix (v0.5.1)**:
   - Renamed auth cookie from "session" to "starpunk_session"
   - Fixed redirect loop between dev login and admin dashboard
   - Flask's session cookie no longer conflicts with auth

2. **HTTP 404 error handling (v0.5.1)**:
   - Update route now returns 404 for nonexistent notes
   - Delete route now returns 404 for nonexistent notes
   - Follows ADR-012 HTTP Error Handling Policy
   - Pattern consistency across all admin routes

3. **Note model enhancement (v0.5.2)**:
   - Exposed deleted_at field from database schema
   - Enables soft deletion verification in tests
   - Follows ADR-013 transparency principle

### Architecture

**New ADRs**:
- ADR-011: Development Authentication Mechanism
- ADR-012: HTTP Error Handling Policy
- ADR-013: Expose deleted_at Field in Note Model

**Standards Compliance**:
- Uses uv for Python environment
- Black formatted, Flake8 clean
- Follows git branching strategy
- Version incremented per versioning strategy

### Test Results

- 405/406 tests passing (99.75%)
- 87% code coverage
- All security tests passing
- Manual testing confirmed working

### Documentation

- Complete implementation reports in docs/reports/
- Architecture reviews in docs/reviews/
- Design documents in docs/design/
- CHANGELOG updated for v0.5.2

### Files Changed

**New Modules**:
- starpunk/dev_auth.py
- starpunk/routes/ (public, admin, auth, dev_auth)

**Templates**: 10 files (base, pages, admin, errors)
**Static**: CSS and optional JavaScript
**Tests**: 4 test files for routes and templates
**Docs**: 20+ architectural and implementation documents

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

starpunk/models.py

@@ -57,6 +57,7 @@ class Note:
         published: Whether note is published (visible publicly)
         created_at: Creation timestamp (UTC)
         updated_at: Last update timestamp (UTC)
+        deleted_at: Soft deletion timestamp (UTC, None if not deleted)
         content_hash: SHA-256 hash of content (for integrity checking)
         _data_dir: Base data directory path (used for file loading)
         _cached_content: Cached markdown content (lazy-loaded)
@@ -111,6 +112,7 @@ class Note:
     _data_dir: Path = field(repr=False, compare=False)
 
     # Optional fields
+    deleted_at: Optional[datetime] = None
     content_hash: Optional[str] = None
     _cached_content: Optional[str] = field(
         default=None, repr=False, compare=False, init=False
@@ -150,6 +152,10 @@ class Note:
         if isinstance(updated_at, str):
             updated_at = datetime.fromisoformat(updated_at.replace("Z", "+00:00"))
 
+        deleted_at = data.get("deleted_at")
+        if deleted_at and isinstance(deleted_at, str):
+            deleted_at = datetime.fromisoformat(deleted_at.replace("Z", "+00:00"))
+
         return cls(
             id=data["id"],
             slug=data["slug"],
@@ -157,6 +163,7 @@ class Note:
             published=bool(data["published"]),
             created_at=created_at,
             updated_at=updated_at,
+            deleted_at=deleted_at,
             _data_dir=data_dir,
             content_hash=data.get("content_hash"),
         )