fix(gateway): persist memory flush state to prevent redundant re-flushes on restart (#4481)

* fix: force-close TCP sockets on client cleanup, detect and recover dead connections

When a provider drops connections mid-stream (e.g. OpenRouter outage),
httpx's graceful close leaves sockets in CLOSE-WAIT indefinitely. These
zombie connections accumulate and can prevent recovery without restarting.

Changes:
- _force_close_tcp_sockets: walks the httpx connection pool and issues
  socket.shutdown(SHUT_RDWR) + close() to force TCP RST on every socket
  when a client is closed, preventing CLOSE-WAIT accumulation
- _cleanup_dead_connections: probes the primary client's pool for dead
  sockets (recv MSG_PEEK), rebuilds the client if any are found
- Pre-turn health check at the start of each run_conversation call that
  auto-recovers with a user-facing status message
- Primary client rebuild after stale stream detection to purge pool
- User-facing messages on streaming connection failures:
  "Connection to provider dropped — Reconnecting (attempt 2/3)"
  "Connection failed after 3 attempts — try again in a moment"

Made-with: Cursor

* fix: pool entry missing base_url for openrouter, clean error messages

- _resolve_runtime_from_pool_entry: add OPENROUTER_BASE_URL fallback
  when pool entry has no runtime_base_url (pool entries from auth.json
  credential_pool often omit base_url)
- Replace Rich console.print for auth errors with plain print() to
  prevent ANSI escape code mangling through prompt_toolkit's stdout patch
- Force-close TCP sockets on client cleanup to prevent CLOSE-WAIT
  accumulation after provider outages
- Pre-turn dead connection detection with auto-recovery and user message
- Primary client rebuild after stale stream detection
- User-facing status messages on streaming connection failures/retries

Made-with: Cursor

* fix(gateway): persist memory flush state to prevent redundant re-flushes on restart

The _session_expiry_watcher tracked flushed sessions in an in-memory set
(_pre_flushed_sessions) that was lost on gateway restart. Expired sessions
remained in sessions.json and were re-discovered every restart, causing
redundant AIAgent runs that burned API credits and blocked the event loop.

Fix: Add a memory_flushed boolean field to SessionEntry, persisted in
sessions.json. The watcher sets it after a successful flush. On restart,
the flag survives and the watcher skips already-flushed sessions.

- Add memory_flushed field to SessionEntry with to_dict/from_dict support
- Old sessions.json entries without the field default to False (backward compat)
- Remove the ephemeral _pre_flushed_sessions set from SessionStore
- Update tests: save/load roundtrip, legacy entry compat, auto-reset behavior

cli.py

@@ -1979,10 +1979,12 @@ class HermesCLI:
                     base_url, _source,
                 )
             else:
-                self.console.print("[bold red]Provider resolver returned an empty API key.[/]")
+                print("\n⚠️  Provider resolver returned an empty API key. "
+                      "Set OPENROUTER_API_KEY or run: hermes setup")
                 return False
         if not isinstance(base_url, str) or not base_url:
-            self.console.print("[bold red]Provider resolver returned an empty base URL.[/]")
+            print("\n⚠️  Provider resolver returned an empty base URL. "
+                  "Check your provider config or run: hermes setup")
             return False
 
         credentials_changed = api_key != self.api_key or base_url != self.base_url