fix(ci): resolve follow-up title edge case and flaky checks

Handle queued-title ValueError cleanup during session init, harden Discord message source building for test stubs, and fix the Dockerfile contract test syntax error. Also refresh the TUI lockfile and Nix build flags so nix ubuntu-latest no longer fails on npm lock/peer resolution drift.

tests/tools/test_dockerfile_pid1_reaping.py

@@ -39,7 +39,8 @@ def _dockerfile_instructions(dockerfile_text: str) -> list[str]:
         if not line or line.startswith("#"):
             continue
 
-        current = f"{current} {line.removesuffix('\\').strip()}".strip()
+        continued = line.removesuffix("\\").strip()
+        current = f"{current} {continued}".strip()
         if not line.endswith("\\"):
             instructions.append(current)
             current = ""