feat(prompts): implement Phase 7 - Quality & Validation (FR-9, FR-10)

Add quality gate framework with schema validation (JSON Schema via
jsonschema library), pattern validation (regex-based), multi-gate
QualityValidator with SQLite persistence, HaltingPolicyEngine with
budget/iteration/improvement checks, and RefinementLoop for iterative
execute-validate-halt cycles.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

migrations/prompts/006_create_quality_tables.sql

@@ -0,0 +1,25 @@
+-- Phase 7: Quality & Validation tables
+-- quality_gates: registered quality gate configurations
+-- validation_results: recorded pass/fail results from gate checks
+
+CREATE TABLE IF NOT EXISTS quality_gates (
+    id TEXT PRIMARY KEY,
+    name TEXT NOT NULL,
+    gate_type TEXT NOT NULL,
+    config JSON NOT NULL,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE TABLE IF NOT EXISTS validation_results (
+    id TEXT PRIMARY KEY,
+    run_id TEXT NOT NULL,
+    gate_id TEXT NOT NULL,
+    artifact_id TEXT,
+    status TEXT NOT NULL,
+    score REAL,
+    diagnostics JSON,
+    validated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE INDEX IF NOT EXISTS idx_validations_run ON validation_results(run_id);
+CREATE INDEX IF NOT EXISTS idx_validations_artifact ON validation_results(artifact_id);