ai_runs logging, redaction and retention (#60)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>

docs/ARCHITECTURE.md

@@ -150,7 +150,18 @@ automatic** (D-021).
   Anthropic and Ollama endpoints, called over plain HTTP — no vendor SDKs.
 - **Skill harness** (`ai/harness`): prompt layering, validation of the
   structured output, and **one repair retry**; if the repair also fails the
-  run fails — no silent fallback. Every call is recorded in `ai_runs`.
+  run fails — no silent fallback. Every run writes one `ai_runs` row when it
+  ends, covering the repair turn too, with status `ok`, `repaired`,
+  `bad_output` or `provider_error`; a prompt that cannot be rendered is
+  `bad_output` and a provider that cannot be built is `provider_error`, both
+  with no turns. The harness builds the provider itself from the settings
+  and the decrypted API key (`presets.FromSettings`), so the key it redacts
+  is always the key the provider sends. Request and response
+  bodies are redacted before they are stored: the decrypted API key,
+  Authorization and API-key header values, Google Chat webhook URLs and URLs
+  with key-like query parameters are removed, inside JSON strings too.
+  `harness.Purge` deletes rows older than `harness.RunRetention` (30 days),
+  clearing the `suggestion_batches` and `week_plans` references first.
 - **Prompt layering** (D-007): each skill version's prompt is a
   `text/template` file embedded from `ai/skills/prompts/`
   (`<skill>.v<version>.tmpl`). The system prompt is always, in order: