0.34.0: stack log viewer — fixed height, container filter, severity coloring

Frontend-only release. Overhauls the stack Logs tab:
- Fix the log panel growing down the page (AppShell <main> has no definite
  height, so the page h-full/flex-1 chain collapsed to auto): the scroll
  area now uses a fixed h-[65vh] instead of flex-1.
- Filter by container (service <select>) plus a free-text search; the line
  count shows filtered / total.
- Dozzle-style per-line severity coloring (error/warn/debug via regex).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/package.json

@@ -1,7 +1,7 @@
 {
   "name": "stackpilot-frontend",
   "private": true,
-  "version": "0.33.0",
+  "version": "0.34.0",
   "type": "module",
   "scripts": {
     "dev": "vite",