fix: persist and recover the Agent's real installation_id (heartbeat activation)

POST /v1/agents/enroll now returns installation_id; new installs persist it
to agent.env immediately. Runtime recovery precedence: existing SQLite
installation_identity -> configured INSTALLATION_ID -> authenticated
GET /v1/agents/me/identity. Recovery fails closed on missing/malformed/
mismatched identity rather than inventing a UUID (which the Hub would then
reject as a conflicting Installation on an already-enrolled Agent). An
explicit AGENT_JOBS_ENABLED gate stops the service from claiming a job right
after the first heartbeat.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

agent/service/gti_agent_windows_service.py

@@ -87,7 +87,15 @@ if win32serviceutil is not None:
 def main():
     if win32serviceutil is None:
         raise SystemExit("pywin32 is required: pip install pywin32")
-    win32serviceutil.HandleCommandLine(GTIFiscalAgentService)
+    if len(sys.argv) == 1:
+        # SCM launches a service executable without CLI arguments. HandleCommandLine
+        # requires a command (install/start/debug) and exits with usage when none
+        # is present, which makes SCM report error 1053 for a frozen service host.
+        servicemanager.Initialize()
+        servicemanager.PrepareToHostSingle(GTIFiscalAgentService)
+        servicemanager.StartServiceCtrlDispatcher()
+    else:
+        win32serviceutil.HandleCommandLine(GTIFiscalAgentService)
 
 
 if __name__ == "__main__":