Update idle time configuration to improve resource management

- Reduced default values for IDLE_MINUTES from 60 to 30 and IDLE_GRACE_MINUTES from 90 to 45 across configuration files and documentation.
- Updated related documentation to reflect the new default idle time settings, ensuring consistency in user guidance and system behavior.

src/gpu_rent/remote/idle_killer.py

@@ -242,7 +242,7 @@ def main() -> int:
 
     now = time.time()
     grace_from = float(creds.get("grace_from") or 0)
-    grace_minutes = float(creds.get("grace_minutes") or 90)
+    grace_minutes = float(creds.get("grace_minutes") or 45)
     if now < grace_from + grace_minutes * 60:
         left = int(grace_from + grace_minutes * 60 - now)
         log(f"grace {left}s left")
@@ -269,7 +269,7 @@ def main() -> int:
         log(f"busy: {llm_detail}")
         return 0
 
-    idle_minutes = float(creds.get("idle_minutes") or 60)
+    idle_minutes = float(creds.get("idle_minutes") or 30)
     since = read_ts(IDLE_SINCE)
     if since is None:
         write_ts(IDLE_SINCE, now)