feat: generic MetadataStore + read_release_metadata + query_library

- Extract MetadataStore from SubtitleMetadataStore (alfred/infrastructure/metadata/).
  Generic load/save + typed update helpers (update_parse, update_probe, update_tmdb)
  for the per-release .alfred/metadata.yaml.
- SubtitleMetadataStore becomes a thin facade — owns subtitle_history shape,
  delegates I/O to MetadataStore.
- Agent._execute_tool_call auto-persists successful analyze_release / probe_media /
  find_media_imdb_id results to the release's .alfred file. find_media_imdb_id
  follows release_focus when it has no path argument.
- New tools:
  · read_release_metadata(release_path) — cacheable, key=release_path.
    Returns the .alfred content or has_metadata=false.
  · query_library(name) — substring scan across configured library roots.
- Both new tools added to CORE_TOOLS (always visible).

alfred/agent/tools/specs/query_library.yaml

@@ -0,0 +1,54 @@
+name: query_library
+
+summary: >
+  Find release folders across all configured library roots whose name
+  contains a substring (case-insensitive).
+
+description: |
+  Scans every configured library root (movies, tv_shows, …) at depth 1
+  and returns folders whose name contains the query. For each match,
+  reports whether a `.alfred/metadata.yaml` exists — handy to spot
+  releases that have not been inspected yet. Does not recurse into
+  seasons / episodes; one entry per release folder.
+
+when_to_use: |
+  - To answer "do I already have X?" without listing whole library
+    roots one by one.
+  - To pick the release_path to feed read_release_metadata or any
+    inspector tool.
+
+when_not_to_use: |
+  - To list the *whole* library — that scan should live behind a
+    dedicated tool (not implemented yet).
+  - To browse a single root — use list_folder instead, it's cheaper
+    and doesn't open every library.
+
+next_steps: |
+  - When one match is found: feed its path to read_release_metadata or
+    analyze_release.
+  - When several match: surface the indexed list to the user and ask
+    which one they mean.
+
+parameters:
+  name:
+    description: Case-insensitive substring of the release name to look for.
+    why_needed: |
+      Library folders are named after the release (Title.Year.... or
+      Title (Year)). A substring is enough to catch typical user
+      phrasings ("foundation", "inception 2010").
+    example: foundation
+
+returns:
+  ok:
+    description: Scan completed (possibly zero matches).
+    fields:
+      status: "'ok'"
+      query: The query string as received.
+      match_count: Number of matching folders.
+      matches: "List of {collection, name, path, has_metadata}."
+
+  error:
+    description: Scan could not run.
+    fields:
+      error: Short error code (no_libraries, empty_name).
+      message: Human-readable explanation.