Task #589: Live build stamp + server start time in System Updates panel

Problem: After `git pull && docker compose up -d --build api` on the
Mac, the admin → System Updates panel kept showing the same version
(0.1.0-dev) and the same build (20260517.b5efd9eb) because both come
from version.json, a hand-edited file that nothing rewrites on every
build. No visible signal that a new image was actually running.

Two independent signals were added — neither needs editing version.json
by hand:

1) Auto-stamp version.json at Docker build time
   - docker/api-server.Dockerfile: new ARGs GIT_SHA and BUILD_DATE.
     A `node -e` step rewrites version.json's `build` field to
     `${YYYYMMDDTHHmm}.${sha}` (e.g. 20260518T1042.a34eb5f5). When
     the args are missing/"unknown", version.json is left untouched
     so plain `docker build` and Replit `pnpm dev` still work.
   - docker-compose.yml: api.build.args wires through GIT_SHA and
     BUILD_DATE with `${GIT_SHA:-unknown}` fallbacks.
   - scripts/redeploy.sh: exports GIT_SHA (git rev-parse --short HEAD)
     and BUILD_DATE (date -u +%Y-%m-%dT%H:%M:%SZ) before `docker
     compose build`, so the helper script just works.

2) startedAt timestamp from the API
   - artifacts/api-server/src/routes/system.ts: SERVER_STARTED_AT
     captured at module load (frozen for the process lifetime) and
     added to every branch of GET /system/version (not-configured,
     error, invalid-version, up-to-date, update-available, catch).
   - lib/api-spec/openapi.yaml: added `startedAt: date-time` to
     SystemVersionResponse (required). Regenerated api-client-react
     and api-zod via `pnpm --filter @workspace/api-spec run codegen`.

3) Admin UI surfacing both signals
   - artifacts/tx-os/src/pages/admin.tsx: new formatBuildStamp parses
     `YYYYMMDD[THHmm].sha` and renders a localized date next to the
     raw token. A new "Server started" line below the build number
     formats the boot timestamp via the existing formatChecked helper.
   - artifacts/tx-os/src/locales/{en,ar}.json: added
     admin.systemUpdates.serverStartedAt ("Server started" /
     "بدأ تشغيل الخادم").

4) Docs
   - replit.md: documented how to verify a real redeploy via the
     System Updates panel and the manual one-liner for `docker
     compose build` without the helper script.

Verified: codegen succeeds, API workflow restarted clean, Vite served
fine. Pre-existing typecheck errors in push.ts and font-settings are
unrelated and untouched.

Mac next steps:
  cd ~/Downloads/TX && git pull && ./scripts/redeploy.sh
Then open admin → System Updates: build line should show a new
`YYYYMMDDTHHmm.sha` stamp and "Server started" should reflect the
new boot time.

artifacts/api-server/src/routes/system.ts

@@ -9,6 +9,12 @@ const router: IRouter = Router();
 const CURRENT_VERSION: string = versionFile.version;
 const CURRENT_BUILD: string = versionFile.build;
 
+// Captured once at module load — frozen for the lifetime of the
+// process. The admin "System Updates" panel renders this so the user
+// gets a visible signal whenever the container actually restarts
+// (independent of build/version, which only change on rebuild).
+const SERVER_STARTED_AT: string = new Date().toISOString();
+
 const LATEST_URL = process.env.LATEST_VERSION_URL ?? "";
 const FETCH_TIMEOUT_MS = 5000;
 
@@ -29,6 +35,7 @@ router.get("/system/version", requireAdmin, async (_req, res): Promise<void> =>
         errorMessage: null,
         checkedAt,
         configured: false,
+          startedAt: SERVER_STARTED_AT,
       }),
     );
     return;
@@ -50,6 +57,7 @@ router.get("/system/version", requireAdmin, async (_req, res): Promise<void> =>
           errorMessage: `HTTP ${response.status}`,
           checkedAt,
           configured: true,
+          startedAt: SERVER_STARTED_AT,
         }),
       );
       return;
@@ -68,6 +76,7 @@ router.get("/system/version", requireAdmin, async (_req, res): Promise<void> =>
           errorMessage: "Invalid version format",
           checkedAt,
           configured: true,
+          startedAt: SERVER_STARTED_AT,
         }),
       );
       return;
@@ -86,6 +95,7 @@ router.get("/system/version", requireAdmin, async (_req, res): Promise<void> =>
         errorMessage: null,
         checkedAt,
         configured: true,
+          startedAt: SERVER_STARTED_AT,
       }),
     );
   } catch (err) {
@@ -103,6 +113,7 @@ router.get("/system/version", requireAdmin, async (_req, res): Promise<void> =>
         errorMessage: message,
         checkedAt,
         configured: true,
+          startedAt: SERVER_STARTED_AT,
       }),
     );
   } finally {