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

knowledge/cache-telemetry-recipe.md

@@ -109,6 +109,6 @@ when structural signal alone isn't enough.
 
 ## See also
 
-- `knowledge/opus-4.7-patterns.md` — structural patterns the TOK scanner detects (CA-TOK-001..005)
+- `knowledge/prompt-cache-patterns.md` — structural patterns the TOK scanner detects (CA-TOK-001..005)
 - `knowledge/configuration-best-practices.md` — CLAUDE.md cache-stability guidance
 - `/config-audit tokens --with-telemetry-recipe` — surfaces a pointer to this file in JSON output