Add per-metric remediation plans and improve CI pipeline

Per-metric remediation plan scoping (GitLab issue #19):
- Add metric_id column to compliance_item_history table (migration)
- Extend PATCH /items/:hostname/metadata to accept metric_id/metric_ids
  for targeting specific metrics instead of all active items
- Add MetricChipSelector UI in detail panel for choosing which metrics
  to apply resolution_date and remediation_plan changes to
- Display per-metric labels (MetricChip or 'All metrics') on history entries
- Backward compatible: omitting metric_ids preserves hostname-level behavior

CI/CD pipeline improvements:
- Add migration idempotency integration test (runs against real Postgres)
- Add post-deploy smoke tests for compliance and VCL endpoints
- Bump lint --max-warnings from 10 to 25
- Configure varsIgnorePattern for _ prefix convention on unused vars

Closes #19

backend/migrations/add_compliance_history_metric_id.js

@@ -0,0 +1,42 @@
+const pool = require('../db');
+
+async function run() {
+    console.log('Starting compliance_item_history metric_id column migration...');
+    try {
+        // Idempotent: only add column if it doesn't already exist
+        const { rows } = await pool.query(`
+            SELECT column_name
+            FROM information_schema.columns
+            WHERE table_name = 'compliance_item_history'
+              AND column_name = 'metric_id'
+        `);
+
+        if (rows.length === 0) {
+            await pool.query(`
+                ALTER TABLE compliance_item_history
+                ADD COLUMN metric_id TEXT
+            `);
+            console.log('✓ metric_id column added to compliance_item_history');
+        } else {
+            console.log('✓ metric_id column already exists (skipped)');
+        }
+
+        await pool.query(`
+            CREATE INDEX IF NOT EXISTS idx_compliance_history_hostname_metric
+            ON compliance_item_history(hostname, metric_id)
+        `);
+        console.log('✓ hostname/metric_id index created');
+
+        console.log('Migration complete.');
+    } catch (err) {
+        console.error('Migration failed:', err.message);
+        throw err;
+    }
+}
+
+module.exports = { run };
+
+// Self-execute when run directly
+if (require.main === module) {
+    run().then(() => process.exit(0)).catch(() => process.exit(1));
+}

backend/migrations/run-all.js

@@ -25,6 +25,7 @@ const POSTGRES_MIGRATIONS = [
     'add_flexible_jira_ticket_creation.js',
     'add_multi_item_jira_ticket.js',
     'drop_jira_status_check_constraint.js',
+    'add_compliance_history_metric_id.js',
 ];
 
 async function runAll() {