test(microformats): Add v1.3.0 validation tests for tags and h-feed

Phase 4: Validation per microformats-tags-design.md

Added test fixtures:
- published_note_with_tags: Creates note with test tags for p-category validation
- published_note_with_media: Creates note with media for u-photo placement testing

Added v1.3.0 microformats2 validation tests:
- test_hfeed_has_required_properties: Validates name, author, url per spec
- test_hfeed_author_is_valid_hcard: Validates h-card structure
- test_hentry_has_pcategory_for_tags: Validates p-category markup
- test_uphoto_outside_econtent: Validates u-photo placement per draft spec

Test results:
- All 18 microformats tests pass
- All 116 related tests pass (microformats, notes, micropub)
- Confirms Phases 1-3 implementation correctness

Updated BACKLOG.md with tag-filtered feeds feature (medium priority)

Implementation report: docs/design/v1.3.0/2025-12-10-phase4-implementation.md

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

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

tests/conftest.py

@@ -64,3 +64,41 @@ def sample_note(app):
             published=True,
         )
         return note
+
+
+@pytest.fixture
+def published_note_with_tags(app):
+    """Create a published note with tags for microformats testing (v1.3.0)"""
+    from starpunk.notes import create_note
+
+    with app.app_context():
+        note = create_note(
+            content="Test note with tags for microformats validation",
+            published=True,
+            tags=["Python", "IndieWeb", "Testing"]
+        )
+        return note
+
+
+@pytest.fixture
+def published_note_with_media(app):
+    """Create a published note with media for u-photo testing (v1.3.0)"""
+    from starpunk.notes import create_note
+    from starpunk.media import save_media, attach_media_to_note
+    from PIL import Image
+    import io
+
+    with app.app_context():
+        note = create_note(content="Test note with media", published=True)
+
+        # Create minimal valid JPEG for testing
+        img = Image.new('RGB', (100, 100), color='red')
+        img_bytes = io.BytesIO()
+        img.save(img_bytes, format='JPEG')
+        img_bytes.seek(0)
+
+        # Save media and attach to note
+        media_info = save_media(img_bytes.getvalue(), 'test.jpg')
+        attach_media_to_note(note.id, [media_info['id']], ['Test image'])
+
+        return note