feat(sessions): add --source flag for third-party session isolation (#3255)

When third-party tools (Paperclip orchestrator, etc.) spawn hermes chat
as a subprocess, their sessions pollute user session history and search.

- hermes chat --source <tag> (also HERMES_SESSION_SOURCE env var)
- exclude_sources parameter on list_sessions_rich() and search_messages()
- Sessions with source=tool hidden from sessions list/browse/search
- Third-party adapters pass --source tool to isolate agent sessions

Cherry-picked from PR #3208 by HenkDz.

Co-authored-by: Henkey <noonou7@gmail.com>

run_agent.py

@@ -883,7 +883,7 @@ class AIAgent:
             try:
                 self._session_db.create_session(
                     session_id=self.session_id,
-                    source=self.platform or "cli",
+                    source=self.platform or os.environ.get("HERMES_SESSION_SOURCE", "cli"),
                     model=self.model,
                     model_config={
                         "max_iterations": self.max_iterations,
@@ -4859,7 +4859,7 @@ class AIAgent:
                 self.session_id = f"{datetime.now().strftime('%Y%m%d_%H%M%S')}_{uuid.uuid4().hex[:6]}"
                 self._session_db.create_session(
                     session_id=self.session_id,
-                    source=self.platform or "cli",
+                    source=self.platform or os.environ.get("HERMES_SESSION_SOURCE", "cli"),
                     model=self.model,
                     parent_session_id=old_session_id,
                 )