Add path canonicalization to prevent symlink duplicates

Implements centralized path canonicalization to ensure symlinks and paths
with . or .. segments are resolved to their canonical form, preventing
false duplicate detection.

Changes to utils.py:
- Add canonical_path() function using Path.resolve()
- Add canonical_path_str() for dictionary key usage

Changes to models.py:
- Add __post_init__ to VideoFile to auto-canonicalize paths
- All VideoFile instances now have canonical paths automatically

Impact:
- Path-based dictionary lookups now work correctly with symlinks
- io.py: path_to_inventory dictionary uses canonical keys
- planner.py: path_to_index dictionary uses canonical keys
- analysis.py: Duplicate detection uses canonical paths
- No false duplicates from symlinks or relative paths

Testing:
- Added comprehensive tests for canonical_path functions
- Tests verify symlink resolution, absolute path conversion, .. removal
- All 449 tests pass (added 10 new tests)

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

src/vlm/models.py

@@ -13,9 +13,9 @@ from typing import Optional
 @dataclass
 class VideoFile:
     """Represents a video file discovered during inventory scanning.
-    
+
     Attributes:
-        path: Full path to the video file
+        path: Full path to the video file (automatically canonicalized)
         filename: Name of the file (without directory path)
         size_bytes: File size in bytes
         modified_timestamp: Last modification timestamp
@@ -30,13 +30,18 @@ class VideoFile:
     size_bytes: int
     modified_timestamp: datetime
     category: str
-    
+
     # Optional metadata (if ffprobe available)
     resolution: Optional[str] = None
     codec: Optional[str] = None
     duration_seconds: Optional[float] = None
     bitrate_kbps: Optional[int] = None
 
+    def __post_init__(self):
+        """Canonicalize path on creation."""
+        from vlm.utils import canonical_path
+        object.__setattr__(self, 'path', canonical_path(self.path))
+
 
 @dataclass
 class MovieIdentity:

src/vlm/utils.py

@@ -1,6 +1,7 @@
 """Shared utilities for Video Library Manager."""
 
 from datetime import datetime, timezone
+from pathlib import Path
 
 
 def utc_now() -> datetime:
@@ -22,3 +23,27 @@ def format_size(size_bytes: int) -> str:
             return f"{size_bytes:.1f} {unit}"
         size_bytes /= 1024.0
     return f"{size_bytes:.1f} PB"
+
+
+def canonical_path(path: Path) -> Path:
+    """Return canonical absolute path, resolving symlinks.
+
+    Args:
+        path: Path to canonicalize
+
+    Returns:
+        Canonical absolute path with symlinks resolved
+    """
+    return path.resolve()
+
+
+def canonical_path_str(path: Path) -> str:
+    """Return canonical path as string for use as dictionary key.
+
+    Args:
+        path: Path to canonicalize
+
+    Returns:
+        String representation of canonical path
+    """
+    return str(canonical_path(path))