feat(media-use): agent-driven asset reuse (candidates + reuse)

Reuse now hands the semantic judgment to the coding agent instead of a
string heuristic, while keeping the deterministic normalize-exact match as
an automatic dedup floor. No LLM/embedding call enters resolve; it stays
offline-capable.

- lib/match.mjs: shared matchTokens + typesMatch (extracted from adopt.mjs
  and resolve.mjs so the icon<->image equivalence and token rules can't
  drift between the do-path and the look-path); adds tokenOverlap ranker.
- resolve --candidates: side-effect-free listing of reusable assets across
  the project manifest AND the global ~/.media cache, ranked by lexical
  overlap, capped per scope, --json or human table. Never hard-filters on
  zero overlap (that would pre-empt the agent's judgment); the agent decides.
- resolve --reuse <sha>: import a specific global-cache asset by content
  sha/prefix (from --candidates) into the project via importFromCache,
  marked source=reused-explicit / provenance.reused_by=agent.
- Adherence nudge: on a resolve that misses the exact floor and is about to
  fetch, print a one-line stderr hint when similar cached assets exist,
  pointing at --candidates. Offline, stderr (safe under --json), never
  auto-reuses a fuzzy match.
- cache.mjs: export readGlobalManifest; add findGlobalBySha (prefix resolve
  with ambiguity/miss handling).
- Telemetry: media_use_candidates event + reused-explicit source on
  media_use_resolve (type/scope/counts only, no intent text or paths).
- SKILL.md: 'Reuse before you resolve' guidance + trust guardrail
  (prefer-fresh-when-unsure, entity-exact for brand, cross-project bleed).
- Tests: lib/candidates.test.mjs (ranking, no-hard-filter, cap/truncation,
  icon<->image, sha resolution, formatter); adopt.mjs refactor covered by
  existing lib/adopt.test.mjs.

Full media-use suite green; verified e2e against the live catalog
(cross-project resolve->candidates->reuse; hint fires on miss).

skills/media-use/scripts/lib/adopt.mjs

@@ -3,6 +3,7 @@ import { join, extname, basename } from "node:path";
 import { readManifest, appendRecord, nextId } from "./manifest.mjs";
 import { regenerateIndex } from "./index-gen.mjs";
 import { probe } from "./probe.mjs";
+import { matchTokens } from "./match.mjs";
 
 const AUDIO_EXT = new Set([".mp3", ".wav", ".ogg", ".m4a", ".aac"]);
 const IMAGE_EXT = new Set([".jpg", ".jpeg", ".png", ".gif", ".webp", ".svg", ".ico"]);
@@ -96,30 +97,6 @@ export function adoptExistingAssets(projectDir) {
   return adopted;
 }
 
-// Common filler words that should never, on their own, make a filename match an
-// intent (e.g. intent "the rocket" must not adopt "the-video.mp4").
-const MATCH_STOPWORDS = new Set([
-  "the",
-  "and",
-  "for",
-  "with",
-  "from",
-  "this",
-  "that",
-  "your",
-  "our",
-]);
-
-// Split into lowercased word tokens of length >= 3, minus stopwords.
-function matchTokens(text) {
-  return new Set(
-    String(text)
-      .toLowerCase()
-      .split(/[^a-z0-9]+/)
-      .filter((t) => t.length >= 3 && !MATCH_STOPWORDS.has(t)),
-  );
-}
-
 // Adopt a pre-existing assets/ file only when it shares a meaningful word with
 // the intent. The old test — `name.includes(intent) || intent.includes(name)` —
 // silently returned the WRONG file: "whoosh" grabbed a stray who.mp3, and a