feat(m14): AI assistant — explain diagnostics, opt-in (Ollama or Claude) — 0.27.0

New optional module (D24): explains the collected findings in plain language,
contacted ONLY on an explicit user action (never automatic).

- core/ai.py: provider chosen explicitly (no default) — ollama (local) or claude
  (Anthropic Messages API via stdlib urllib; key in keyring). Grounded prompt;
  HTTP error parsing; one-shot (no thinking/caching — snappy).
- core/ai_knowledge.py: curated reference KB (Xid/SMART/Proton/tunables),
  exact keyword/code match ("RAG-lite", no embeddings) injected into the prompt —
  lifts local models, sharpens Claude. No fine-tuning.
- config: ai_provider/ai_model/ai_endpoint + keyring-backed AI key (generalized
  the token keyring helpers).
- GUI: Settings → AI assistant (provider radios, model/endpoint/key, Save/Test);
  "Explain with AI" button on the diagnostic dialog (consent prompt for cloud).
- CLI: `rigdoctor ai status|test|explain`.
- Docs: D24, SPEC/MODULES/ROADMAP (Phase 7); tests for providers/grounding/parse.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/ROADMAP.md

@@ -89,6 +89,14 @@ Ubuntu + NVIDIA first; `.deb` distribution (see `DECISIONS.md`).
 - [removed] The read-only stats view (`share serve`) and bundle export — dropped per D23; the
       shared terminal is the only sharing mode.
 
+## Phase 7 — AI assistant  (M14, D24)
+- [x] **Explain diagnostics with AI** — opt-in, never automatic (`core/ai.py`, "Explain with AI"
+      button + `rigdoctor ai explain`). Provider chosen explicitly: **Ollama** (local) or
+      **Claude** (Anthropic). Grounded with a curated reference KB (`core/ai_knowledge.py`,
+      RAG-lite, exact match — no embeddings); stdlib `urllib`. Settings → AI assistant.
+- [ ] *Possible follow-ups:* interactive chat grounded in the data; more reference-KB entries;
+      an "Explain" button on the System Health page.
+
 > **Out of scope:** stress/repro module (D7); multi-distro support and packaging beyond
 > Ubuntu/apt + `.deb` (D15) — a thin seam is kept but not built out.