ci: add timeouts to all CI/CD jobs, Dagger tasks, and runner scripts (#432)

Closes #415

## Summary

- Adds missing `timeout-minutes` to `ci.yml` (`check` job, 60 min) and `windows-nightly.yml` (90 min, ready for when the Windows runner is registered)
- Wraps `ssh-keyscan` and `ssh -f -N -L` tunnel creation in `setup_dagger_remote.sh` with `timeout 30`; emits a `::warning::` annotation when either takes more than 10 s
- Adds `timeout --kill-after=10 <N>` to all bare `dagger call` invocations in `Taskfile.yml`: 600 s for test/query tasks, 1800 s for build/deploy tasks, 60 s for `ci-graph`; `stalwart` and `check-dagger` (already protected) left untouched
- Adds `timeout --kill-after=10 2400` per attempt in `run_firebase_test.sh`; emits `::warning::` on exit 124 instead of silently retrying

## Test plan

- CI passes on this PR (the `check` job now has `timeout-minutes: 60` and will self-enforce)
- All `dagger call` lines in `Taskfile.yml` now have a `timeout` prefix (visible in the diff)
- `setup_dagger_remote.sh` logic is unchanged — only the two network calls are wrapped

Co-authored-by: Thomas SharedInbox <sharedinbox@thomas-guettler.de>
Reviewed-on: https://codeberg.org/guettli/sharedinbox/pulls/432

.forgejo/workflows/ci.yml

@@ -4,6 +4,7 @@ jobs:
   check:
     name: Full Project Check
     runs-on: ubuntu-latest
+    timeout-minutes: 60
     steps:
       - uses: actions/checkout@v4
       - name: Setup Dagger Remote Engine

.forgejo/workflows/windows-nightly.yml

@@ -10,6 +10,7 @@ jobs:
     # Disabled until a self-hosted runner with label "windows-runner" is registered.
     name: Build & Deploy Windows (Nightly)
     runs-on: windows-runner
+    timeout-minutes: 90
     if: false
 
     steps: