security: fix log/state file permissions, Firebase key on disk, TLS cleanup

- agent_loop.py: create log dir with mode 0700 and enforce it on
  existing dirs; open log files with mode 0600; chmod state file
  to 0600 after every write. Prevents other local processes from
  reading agent output (which may contain credential paths) or
  tampering with the state file's pid field.

- ci/main.go (TestAndroidFirebase): replace
    echo "$FIREBASE_SA_KEY" > /tmp/key.json
  with bash process substitution
    --key-file=<(echo "$FIREBASE_SA_KEY")
  The key is now passed via a file descriptor — it never touches
  disk, so it cannot be stranded by a failed gcloud auth call or
  snapshotted into the Dagger layer cache.

- ci.yml / deploy.yml: add "Cleanup TLS credentials" step
  (if: always()) at the end of every job that calls
  setup_dagger_remote.sh. Removes /tmp/dagger-tls,
  /tmp/stunnel-dagger.conf, /tmp/stunnel.pid from the self-hosted
  runner after each job, so client certs do not accumulate between
  job runs.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ci/main.go

@@ -680,10 +680,8 @@ func (m *Ci) TestAndroidFirebase(
 		WithEnvVariable("FIREBASE_PROJECT_ID", projectID).
 		WithExec([]string{"/bin/bash", "-c",
 			`auth_err=$(mktemp); trap 'rm -f "$auth_err"' EXIT; \
-			 echo "$FIREBASE_SA_KEY" > /tmp/key.json; \
-			 gcloud auth activate-service-account --key-file=/tmp/key.json 2>"$auth_err" \
+			 gcloud auth activate-service-account --key-file=<(echo "$FIREBASE_SA_KEY") 2>"$auth_err" \
 			   || { cat "$auth_err"; exit 1; }; \
-			 rm -f /tmp/key.json; \
 			 gcloud config set project "$FIREBASE_PROJECT_ID" 2>>"$auth_err" \
 			   || { cat "$auth_err"; exit 1; }; \
 			 unknown=$(grep -vF "Activated service account credentials for:" "$auth_err" \