[johnnyhuy]

What changed

Adds a deterministic operator-rule matcher so Wingman can return a pinned, approved answer for known questions instead of a generated one. Rules load from config, and the RAG ask path checks them before retrieval and generation.

Part of #6
Closes #15

How it was verified

• mise run install - passed (backend via uv, frontend via bun, runtime deps)
• mise run test-backend - 47 passed, including 21 new tests in backend/tests/test_rules.py
• mise run test-frontend - passed (the repo task currently reports no frontend tests yet)
• Offline HTTP proof against the local backend (see below). Slack auth was stubbed with the repo test pattern, so nothing connected to a live workspace.

Proof

Backend started locally with OPERATOR_RULES_JSON=[{"id":"vpn-reset","keywords":["reset vpn"],"response":"Use the IT portal to reset VPN access."}], a sqlite database and the Pi runtime pointed at a dead local port, so a matched answer can only come from the rule.

Matched question returns the canned answer with the rule as its source:

$ curl -s -X POST http://127.0.0.1:8000/api/ask -H 'Content-Type: application/json' -d '{"question":"How do I reset VPN access?"}'
{"answer":"Use the IT portal to reset VPN access.","sources":[{"source":"operator_rule","rule_id":"vpn-reset"}],"confidence":"high"}

Unmatched question leaves the rule path and enters normal retrieval (fails here only because Chroma is not running in this offline setup):

$ curl -s -X POST http://127.0.0.1:8000/api/ask -H 'Content-Type: application/json' -d '{"question":"What is RAG?"}'
{"detail":"Could not connect to a Chroma server. Are you sure it is running?"}

New tests, all passing: TestMatching (7), TestOrderingAndEnabled (3), TestConfigLoading (9), TestRagShortCircuit (2). The short-circuit tests assert retrieval and generation are never called for a matched question.

Reviewer notes

• Rules cover the /api/ask path through RAGEngine.generate_response in this slice. Slack delivery still goes through the Pi Durable job flow, so wiring rules into the Slack handlers is a follow-up slice. That work would need a live Slack workspace to verify end to end, which this run must not use.
• Bad config fails safe. Invalid rules are logged and skipped, invalid JSON or a missing file loads as no rules, and an empty config is a no-op.
• No migration in this slice. Config is two new settings, OPERATOR_RULES_JSON and OPERATOR_RULES_FILE, documented in .env.example and docs/operator-rules.md.
• One environment note: the worktree venv was recreated with the mise-pinned Python 3.13, because the default Python 3.14 cannot install onnxruntime. No lockfile change was needed and the incidental uv.lock refresh was reverted.