docs(claude): pin excluded_dirs entry-form syntax

The two entry shapes for libraries.excluded_dirs / EXCLUDED_DIRS
are not symmetric:
  - /sub/path → multi-segment, library-root-anchored, recursive
  - name     → single component anywhere in the tree

Without this pinned, a reasonable read of the column doc would be
"any path-like string works" — but a multi-segment string without a
leading slash silently never matches (the no-slash form scans path
components for exact string equality, and components are
slash-free).

No code change; just documentation.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -216,7 +216,15 @@ var, that's applied **in union** with the env-var globals when a
 walker scans this library. Use case: mount a parent directory as a
 new library while a sibling library covers a child subtree, and
 exclude that child subtree from the parent so the two libraries
-don't double-walk and double-write `image_exif`. Hash-keyed derived
+don't double-walk and double-write `image_exif`. Two entry forms
+(parsed by `memories::PathExcluder`):
+- `/sub/path` — leading slash flags it as a path under the library
+  root. Joins to root + matches by `path.starts_with(...)`. Works
+  at any depth (`/photos`, `/media/2024/raw`).
+- `name` — no leading slash flags it as a component name to skip
+  anywhere in the tree (`@eaDir`, `.thumbnails`). Single segment
+  only — `media/photos/a` without a leading slash never matches
+  anything. Hash-keyed derived
 data (faces, tags, insights) is unaffected either way — those
 follow the bytes — but `image_exif` row count, walker CPU, and
 thumbnail disk usage all drop to 1× instead of 2× for the overlap.