feat(abyss-integration): consume abyss skill-manifest for capability discovery (v4.8.0)

[telagod]

Summary

code-abyss 4.8.0 reads abyss's skill-manifest JSON at install time instead of carrying a hand-maintained mirror of abyss's surface. The pre-existing inject/adapter/MCP paths are unchanged — this patch is additive, with fallback to hand-coded defaults whenever the manifest is unavailable.

What discovery actually picks up

Real smoke against abyss 0.5.23:

```
abyss v0.5.23: 19 CLI commands, 8 MCP tools; daemon verbs: ping, stats, reindex, logs, mcp, subscribe

MCP tools (from manifest): search_context, get_symbols, find_callers, impact_analysis,
code_map, evolution, index_project, arch_map ← discovery 自动有
MCP tools (null fallback): search_context, get_symbols, find_callers, impact_analysis,
code_map, evolution, index_project ← hand-coded 漏 arch_map
```

`arch_map` was added to abyss in v0.4.0 but never mirrored in code-abyss. Manifest discovery surfaces it automatically — exactly the kind of drift this patch prevents.

What changed

• `bin/lib/abyss-integration.js`: 3 new exports — `tryReadAbyssManifest`, `summarizeAbyssManifest`, `resolveAbyssMcpTools`. Never-throws, schema_version==1 gated, version-gated at `SKILL_MANIFEST_AVAILABLE_FROM = '0.5.22'`.
• `bin/install.js`: `ensureAbyssBinary` calls `discoverAbyssCapabilities()` and prints the manifest summary after detection or download.
• `MIN_ABYSS_VERSION` bumped `0.3.0` → `0.5.20`: 0.5.x line has been dogfooded across hono/helix/vite/FastAPI/Django/SQLAlchemy. 0.5.22+ unlocks dynamic discovery.
• `package.json` 4.7.2 → 4.8.0 (minor, additive).
• README + CHANGELOG entries.
• 7 new tests including a real-abyss smoke against `/home/telagod/project/code-abyss-dev/target/release/abyss`.

Test plan

• `npm test` (jest): 36 suites passed, 1 skipped, 417 tests passed, 1 skipped (was 411)
• Real-abyss smoke asserts `schema_version === 1` and presence of the `subscribe` daemon verb
• Fallback verified: manifest=null returns the hand-coded 7-tool list
• Version-gate test: 0.5.19 fails MIN, 0.5.20/0.5.23 pass; 0.5.21 < skill-manifest gate
• tryReadAbyssManifest double-gated: explicit binPath still runs `--version` to prevent old-binary noise

Compatibility

abyss not in PATH → fallback. abyss < 0.5.22 → fallback. Manifest parse fail → fallback. Never throws. Existing inject/adapter/MCP registration paths zero-touch.

Sister-project link

Released alongside abyss v0.5.22 (which ships `abyss skill-manifest`) — see https://github.com/telagod/abyss/releases/tag/v0.5.22 and https://github.com/telagod/abyss/releases/tag/v0.5.23.