feat: cap job_runs history at last 10 per job

Tailscale, Patchmon, and Semaphore sync jobs all wrote into a shared
job_runs table with no retention. With default poll intervals of 15-60
minutes, history grew unbounded.

- Add pruneJobRuns(jobId) and pruneAllJobRuns() helpers.
- Prune after every completeJobRun() so new runs trim old ones.
- Prune once on init() to clean up existing over-cap rows.
- Prune in importJobs() so re-imported runs are also capped.
- Defensive LIMIT 10 in getJobRuns() for the read path.

No UI changes needed — _renderRunList already renders whatever the
server returns. No schema migration — only row deletions.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/db.js

@@ -6,6 +6,8 @@ import { fileURLToPath } from 'url';
 const __dirname = dirname(fileURLToPath(import.meta.url));
 const DEFAULT_PATH = join(__dirname, '../data/catalyst.db');
 
+const JOB_RUN_LIMIT = 10;
+
 let db;
 
 function init(path) {
@@ -17,7 +19,7 @@ function init(path) {
   db.exec('PRAGMA foreign_keys = ON');
   db.exec('PRAGMA synchronous = NORMAL');
   createSchema();
-  if (path !== ':memory:') { seed(); seedJobs(); }
+  if (path !== ':memory:') { seed(); seedJobs(); pruneAllJobRuns(); }
 }
 
 function createSchema() {
@@ -267,6 +269,7 @@ export function importJobs(jobRows, jobRunRows = []) {
     `);
     for (const r of jobRunRows) insertRun.run(r);
   }
+  pruneAllJobRuns();
   db.exec('COMMIT');
 }
 
@@ -326,10 +329,28 @@ export function completeJobRun(runId, status, result) {
   db.prepare(`
     UPDATE job_runs SET ended_at=strftime('%Y-%m-%dT%H:%M:%f', 'now'), status=@status, result=@result WHERE id=@id
   `).run({ id: runId, status, result });
+  const row = db.prepare('SELECT job_id FROM job_runs WHERE id = ?').get(runId);
+  if (row) pruneJobRuns(row.job_id);
 }
 
 export function getJobRuns(jobId) {
-  return db.prepare('SELECT * FROM job_runs WHERE job_id = ? ORDER BY id DESC').all(jobId);
+  return db.prepare(`SELECT * FROM job_runs WHERE job_id = ? ORDER BY id DESC LIMIT ${JOB_RUN_LIMIT}`).all(jobId);
+}
+
+function pruneJobRuns(jobId) {
+  db.prepare(`
+    DELETE FROM job_runs
+    WHERE job_id = ?
+      AND id NOT IN (
+        SELECT id FROM job_runs WHERE job_id = ? ORDER BY id DESC LIMIT ?
+      )
+  `).run(jobId, jobId, JOB_RUN_LIMIT);
+}
+
+function pruneAllJobRuns() {
+  for (const j of db.prepare('SELECT id FROM jobs').all()) {
+    pruneJobRuns(j.id);
+  }
 }
 
 // ── Test helpers ──────────────────────────────────────────────────────────────