feat(memory): Phase 1 — STM ToolResultsCache + ReleaseFocus + cache flag in YAML specs

Adds two STM components and a transparent cache hook in the agent loop so
read-only tools don't re-do work the agent already did in this session.

New STM components:
  - ToolResultsCache  — {tool_name: {key: result}}, session-scoped.
    to_dict() exposes only the key inventory (not payloads) to keep the
    prompt cheap.
  - ReleaseFocus      — current_release_path + working_set list, updated
    automatically when a path-keyed inspector runs.

YAML spec layer:
  - New optional 'cache: { key: <param_name> }' block in ToolSpec.
  - Validated at load time: cache.key must be a declared parameter.
  - Surfaced on Tool dataclass as cache_key: str | None.

Agent._execute_tool_call:
  - Pre-exec cache lookup; hit short-circuits and adds _from_cache=true.
  - Post-exec: stores successful results, updates release_focus for
    path-keyed tools, refreshes episodic.last_search_results when
    find_torrent's hit served the response (so get_torrent_by_index
    keeps pointing at the right list).

Cacheable tools (5): analyze_release, probe_media, list_folder,
find_media_imdb_id, find_torrent.

alfred/agent/tools/specs/analyze_release.yaml

@@ -37,6 +37,9 @@ next_steps: |
   - media_type in (other, unknown) → ask the user what to do; do not
     auto-route.
 
+cache:
+  key: source_path
+
 parameters:
   release_name:
     description: Raw release folder or file name as it appears on disk.