🐛 Fix UUOC and missing grep guard in start-runners 🐛

Replaced `echo "$SERVER_ADDRESS" | grep -q '://'` with the native bash
`[[ "$SERVER_ADDRESS" != *"://"* ]]` test, eliminating a useless
subshell/pipe and the missing `--` before the grep pattern that came
with it. Found by the `script-lint` agent while auditing the
act_runner cache-server integration.

- rootfs/usr/local/bin/start-runners: line 24 UUOC fix
- TODO.AI.md: marked the start-runners lint finding fixed; logged a
  new, separate line-length violation on line 36 (`RUNNER_LABELS`
  default is 781 chars) discovered during the same lint pass but not
  yet actioned

rootfs/usr/local/bin/start-runners

@@ -21,7 +21,7 @@ trap __cleanup SIGTERM SIGINT
 # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 # Validate required environment variables
 if [ -n "$SERVER_ADDRESS" ]; then
-	if ! echo "$SERVER_ADDRESS" | grep -q '://'; then
+	if [[ "$SERVER_ADDRESS" != *"://"* ]]; then
 		SERVER_ADDRESS="http://$SERVER_ADDRESS"
 	fi
 else