Fix remote-stack log streaming: URL-encode agent token in WS proxy (0.13.2)

The agent-logs WebSocket proxy injected the agent token raw into the upstream
query string (?token=<token>). Tokens containing base64/url-special characters
(+, /, =) were then mangled by the query parser on the agent side (e.g. "+"
decoded to a space), so the agent rejected the stream with close code 4401 even
though the same token works for the HTTP API (where it travels in the
Authorization header). URL-encode the token with urllib.parse.quote so it
round-trips intact.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/agent_app.py

@@ -40,7 +40,7 @@ from services import backup_service, compose_service
 
 logger = logging.getLogger("stackpilot.agent")
 
-AGENT_VERSION = "0.13.1"
+AGENT_VERSION = "0.13.2"
 
 
 # --------------------------------------------------------------------------- #