feat(slugs): Implement timestamp-based slugs per ADR-062

Replaces content-based slug generation with timestamp format YYYYMMDDHHMMSS.
Simplifies slug generation and improves privacy by not exposing note content in URLs.

Changes:
- Add generate_timestamp_slug() to slug_utils.py
- Update notes.py to use timestamp slugs for default generation
- Sequential collision suffix (-1, -2) instead of random
- Custom slugs via mp-slug continue to work unchanged
- 892 tests passing (+18 new timestamp slug tests)

Per ADR-062 and v1.5.0 Phase 1 specification.

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

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

starpunk/notes.py

@@ -226,15 +226,9 @@ def create_note(
         if not success:
             raise InvalidNoteDataError("slug", custom_slug, error)
     else:
-        # Generate base slug from content
-        base_slug = generate_slug(content, created_at)
-
-        # Make unique if collision
-        slug = make_slug_unique(base_slug, existing_slugs)
-
-        # Validate final slug (defensive check)
-        if not validate_slug(slug):
-            raise InvalidNoteDataError("slug", slug, f"Generated slug is invalid: {slug}")
+        # Generate timestamp-based slug (ADR-062)
+        from starpunk.slug_utils import generate_timestamp_slug
+        slug = generate_timestamp_slug(created_at, existing_slugs)
 
     # 4. GENERATE FILE PATH
     note_path = generate_note_path(slug, created_at, data_dir)

starpunk/slug_utils.py

@@ -241,6 +241,53 @@ def make_slug_unique_with_suffix(base_slug: str, existing_slugs: Set[str], max_a
     )
 
 
+def generate_timestamp_slug(
+    created_at: datetime = None,
+    existing_slugs: Set[str] = None
+) -> str:
+    """Generate a timestamp-based slug with collision handling.
+
+    Per ADR-062: Default format is YYYYMMDDHHMMSS with sequential
+    suffix (-1, -2, etc.) for collisions.
+
+    Args:
+        created_at: Note creation timestamp (defaults to now)
+        existing_slugs: Set of existing slugs to check for collisions
+
+    Returns:
+        Unique timestamp-based slug
+
+    Examples:
+        >>> generate_timestamp_slug(datetime(2025, 12, 16, 14, 30, 52), set())
+        '20251216143052'
+
+        >>> generate_timestamp_slug(datetime(2025, 12, 16, 14, 30, 52), {'20251216143052'})
+        '20251216143052-1'
+
+        >>> generate_timestamp_slug(datetime(2025, 12, 16, 14, 30, 52), {'20251216143052', '20251216143052-1'})
+        '20251216143052-2'
+    """
+    if created_at is None:
+        created_at = datetime.utcnow()
+
+    if existing_slugs is None:
+        existing_slugs = set()
+
+    # Generate base timestamp slug (YYYYMMDDHHMMSS per ADR-062)
+    base_slug = created_at.strftime("%Y%m%d%H%M%S")
+
+    # If no collision, return base slug
+    if base_slug not in existing_slugs:
+        return base_slug
+
+    # Sequential suffix for collisions (starts at -1 per ADR-062)
+    suffix = 1
+    while f"{base_slug}-{suffix}" in existing_slugs:
+        suffix += 1
+
+    return f"{base_slug}-{suffix}"
+
+
 def validate_and_sanitize_custom_slug(custom_slug: str, existing_slugs: Set[str]) -> tuple[bool, Optional[str], Optional[str]]:
     """
     Validate and sanitize a custom slug from Micropub