Initial AI service skeleton

internal/migrate/sql/001_ai_jobs.up.sql

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+CREATE EXTENSION IF NOT EXISTS pgcrypto;
+
+CREATE TABLE IF NOT EXISTS ai_jobs (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    owner_service TEXT NOT NULL,
+    owner_ref TEXT NOT NULL,
+    task_type TEXT NOT NULL,
+    model_profile TEXT NOT NULL,
+    priority INTEGER NOT NULL DEFAULT 0,
+    status TEXT NOT NULL DEFAULT 'pending'
+        CHECK (status IN ('pending', 'running', 'done', 'failed', 'cancelled')),
+    attempts INTEGER NOT NULL DEFAULT 0,
+    max_attempts INTEGER NOT NULL DEFAULT 3,
+    input JSONB NOT NULL DEFAULT '{}'::jsonb,
+    result JSONB,
+    error_code TEXT,
+    error_message TEXT,
+    scheduled_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    started_at TIMESTAMPTZ,
+    completed_at TIMESTAMPTZ,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    idempotency_key TEXT
+);
+
+CREATE UNIQUE INDEX IF NOT EXISTS ai_jobs_idempotency_key_idx
+    ON ai_jobs (idempotency_key)
+    WHERE idempotency_key IS NOT NULL;
+
+CREATE INDEX IF NOT EXISTS ai_jobs_queue_idx
+    ON ai_jobs (status, priority DESC, scheduled_at ASC, created_at ASC)
+    WHERE status IN ('pending', 'running');
+
+CREATE INDEX IF NOT EXISTS ai_jobs_owner_idx
+    ON ai_jobs (owner_service, owner_ref);
+
+CREATE INDEX IF NOT EXISTS ai_jobs_error_idx
+    ON ai_jobs (task_type, model_profile, error_code, updated_at DESC)
+    WHERE status = 'failed';