fix(tokens): refresh stale "Opus 4.7" framing to model-neutral + Opus 4.8 anchor

Fase 4 token-opt, Item 1 of gap-review NEXT STEP #2. The prompt-cache pattern corpus + TOK scanner were frozen at an "Opus 4.7" framing after CC shipped Opus 4.8 (default, 2.1.154) and Fable 5 (2.1.170). Model-era facts re-verified against the official changelog cache before editing.

The patterns are properties of prompt-caching, not of any model, so mechanic text is now model-neutral with a single "current default: Opus 4.8" anchor — preventing a re-freeze at the next model bump.

- rename knowledge/opus-4.7-patterns.md -> prompt-cache-patterns.md (git mv, history preserved); 6 reference sites updated
- TOK scanner: line-318 finding text (human-facing) made model-neutral; header + cache-prefix-scanner + CLI comments refreshed
- configuration-best-practices.md body + footnote 4.7 -> 4.8
- human-facing docs: commands/{tokens,help,manifest}.md, project CLAUDE.md, README, docs/scanner-internals.md
- gap-matrix row marked DONE; future Items 2/3 retargeted to new filename

Failing-test-first (Iron Law): +2 knowledge staleness guards (era-anchor + no-refreeze) +1 scanner assertion (no stale model anchor in finding text). Suite 853 -> 856 green; zero snapshot drift; self-audit A(97) PASS. CHANGELOG / v5 plan / ratified gap-plan keep historical opus-4.7-patterns refs (correct record of past state).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ter3E2JSi1Khgmuf2kady8

tests/knowledge/knowledge-staleness.test.mjs

@@ -92,3 +92,21 @@ test('configuration-best-practices.md recommends real MCP approval, not a `trust
   assert.doesNotMatch(md, /Set trust levels explicitly/,
     'the invented "set trust levels" advice must be gone');
 });
+
+// Token-efficiency corpus era-anchor (Fase 4 token-opt). The prompt-cache pattern
+// catalogue was frozen at an "Opus 4.7" framing after CC shipped Opus 4.8 (default,
+// 2.1.154) and Fable 5 (2.1.170). The mechanics are properties of prompt-caching,
+// not of a model, so the corpus anchors the current default (Opus 4.8) once and
+// keeps the pattern text model-neutral — preventing a re-freeze at the next bump.
+test('prompt-cache pattern catalogue is anchored to Opus 4.8, not frozen at Opus 4.7', () => {
+  const md = read('prompt-cache-patterns.md');
+  assert.match(md, /Opus 4\.8/, 'must name the current default model (Opus 4.8), not a stale 4.7 anchor');
+  assert.doesNotMatch(md, /Opus 4\.7/, 'all stale Opus-4.7 era-stamping must be gone from the pattern catalogue');
+});
+
+test('configuration-best-practices.md CLAUDE.md cost framing names Opus 4.8, not stale 4.7', () => {
+  const md = read('configuration-best-practices.md');
+  assert.match(md, /Opus 4\.8/, 'the cache-vs-length cost-lever framing must name the current default model');
+  assert.doesNotMatch(md, /On Opus 4\.7|Opus 4\.7 uses prompt-cache/,
+    'the present-tense Opus-4.7 cost framing (body + footnote) must be refreshed to 4.8');
+});