🐛 Fix runner config filenames, cache-server, and registration log 🐛

Three more bugs found during full component verification:
1. RUNNER_CONFIG_DEFAULT pointed to config.yaml but the actual
template filename is default_config.yaml — gitea named runner
never registered because the file-existence check always failed.
2. CACHE_CONFIG_FILE pointed to cache.yaml but the actual template
filename is cache_server.yaml — cache-server launch always
skipped silently.
3. act_runner v1.0.6 requires cache.external_secret on both the
cache-server and any runner using external_server; neither config
had it, so cache-server exited immediately and runner registration
failed when external_server was present in default_config.yaml.
4. Registration log redirect was 2>/dev/stdout >>"$log" (stderr went
to original stdout, not the log); corrected to >>"$log" 2>&1.
- rootfs/usr/local/etc/docker/init.d/zz-act_runner.sh:
- RUNNER_CONFIG_DEFAULT: config.yaml → default_config.yaml
- CACHE_CONFIG_FILE: cache.yaml → cache_server.yaml
- fix registration log redirect: >>"$RUNNER_LOG_FILE" 2>&1
- rootfs/tmp/etc/act_runner/default_config.yaml: remove
external_server (no shared secret configured; each runner uses
its own internal cache)
- rootfs/tmp/etc/act_runner/cache_server.yaml: set enabled: false
(cache-server requires external_secret; disabled until a proper
shared-secret setup is added)
Verified: 6 daemons on fresh start (1 gitea named + 5 runners), all
with 22 labels; clean reconnect on restart with no re-registration.

rootfs/tmp/etc/act_runner/cache_server.yaml
rootfs/tmp/etc/act_runner/default_config.yaml
rootfs/usr/local/etc/docker/init.d/zz-act_runner.sh

rootfs/tmp/etc/act_runner/cache_server.yaml

@@ -2,7 +2,7 @@ log:
   level: warn
 
 cache:
-  enabled: true
+  enabled: false
   dir: 'REPLACE_RUNNER_CACHE_DIR'
   host: '0.0.0.0'
   port: REPLACE_RUNNER_CACHE_PORT

rootfs/tmp/etc/act_runner/default_config.yaml

@@ -67,4 +67,3 @@ container:
 
 cache:
   enabled: true
-  external_server: 'http://REPLACE_RUNNER_CACHE_HOST:REPLACE_RUNNER_CACHE_PORT/'