ai_runs logging, redaction and retention (#60)

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

migrations/queries/ai_runs.sql

@@ -0,0 +1,28 @@
+-- name: CreateAIRun :exec
+INSERT INTO ai_runs (
+	id, skill, skill_version, provider, model, temperature, status,
+	latency_ms, tokens_in, tokens_out, error, request_redacted,
+	response_redacted, created_at, updated_at
+) VALUES (
+	?, ?, ?, ?, ?, ?, ?,
+	?, ?, ?, ?, ?,
+	?, ?, ?
+);
+
+-- name: ClearSuggestionBatchAIRunsBefore :execrows
+-- Drops references to the runs created before the cutoff, so the purge
+-- can delete them.
+UPDATE suggestion_batches
+SET ai_run_id = NULL
+WHERE ai_run_id IN (SELECT ai_runs.id FROM ai_runs WHERE ai_runs.created_at < sqlc.arg(cutoff));
+
+-- name: ClearWeekPlanAIRunsBefore :execrows
+-- Drops references to the runs created before the cutoff, so the purge
+-- can delete them.
+UPDATE week_plans
+SET ai_run_id = NULL
+WHERE ai_run_id IN (SELECT ai_runs.id FROM ai_runs WHERE ai_runs.created_at < sqlc.arg(cutoff));
+
+-- name: DeleteAIRunsBefore :execrows
+DELETE FROM ai_runs
+WHERE created_at < sqlc.arg(cutoff);