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/__tests__/migrations-idempotency.integration.test.js

@@ -0,0 +1,83 @@
+// Migration Idempotency Integration Test
+// This test requires a running PostgreSQL instance with DATABASE_URL configured in backend/.env.
+// It runs ALL Postgres migrations twice (via run-all.js) to verify they are idempotent (safe to re-run),
+// then checks that key tables and columns exist.
+//
+// Run separately: npx jest backend/__tests__/migrations-idempotency.integration.test.js --forceExit
+
+const { execSync } = require('child_process');
+const path = require('path');
+
+// The real pool — NOT mocked. This hits the actual database.
+const pool = require('../db');
+
+const BACKEND_DIR = path.join(__dirname, '..');
+
+function runAllMigrations() {
+    execSync('node migrations/run-all.js', {
+        cwd: BACKEND_DIR,
+        stdio: 'pipe',
+        timeout: 30000,
+    });
+}
+
+afterAll(async () => {
+    await pool.end();
+});
+
+describe('Migration Idempotency', () => {
+    it('runs all migrations twice without errors (idempotent)', () => {
+        // First run
+        runAllMigrations();
+        // Second run — should not throw if migrations are truly idempotent
+        runAllMigrations();
+    }, 30000);
+
+    it('key tables exist after migrations', async () => {
+        const expectedTables = [
+            'compliance_items',
+            'compliance_item_history',
+            'compliance_notes',
+            'jira_tickets',
+            'ivanti_fp_submissions',
+        ];
+
+        const { rows } = await pool.query(`
+            SELECT table_name
+            FROM information_schema.tables
+            WHERE table_schema = 'public'
+              AND table_name = ANY($1)
+        `, [expectedTables]);
+
+        const foundTables = rows.map(r => r.table_name);
+        for (const table of expectedTables) {
+            expect(foundTables).toContain(table);
+        }
+    }, 30000);
+
+    it('compliance_item_history has expected columns', async () => {
+        const expectedColumns = [
+            'id',
+            'hostname',
+            'field_name',
+            'old_value',
+            'new_value',
+            'change_reason',
+            'changed_by',
+            'changed_at',
+            'metric_id',
+        ];
+
+        const { rows } = await pool.query(`
+            SELECT column_name
+            FROM information_schema.columns
+            WHERE table_schema = 'public'
+              AND table_name = 'compliance_item_history'
+        `);
+
+        const foundColumns = rows.map(r => r.column_name);
+        for (const col of expectedColumns) {
+            expect(foundColumns).toContain(col);
+        }
+    }, 30000);
+});