fix(honcho): isolate session routing for multi-user gateway (#1500)

Salvaged from PR #1470 by adavyas.

Core fix: Honcho tool calls in a multi-session gateway could route to
the wrong session because honcho_tools.py relied on process-global
state. Now threads session context through the call chain:
  AIAgent._invoke_tool() → handle_function_call() → registry.dispatch()
  → handler **kw → _resolve_session_context()

Changes:
- Add _resolve_session_context() to prefer per-call context over globals
- Plumb honcho_manager + honcho_session_key through handle_function_call
- Add sync_honcho=False to run_conversation() for synthetic flush turns
- Pass honcho_session_key through gateway memory flush lifecycle
- Harden gateway PID detection when /proc cmdline is unreadable
- Make interrupt test scripts import-safe for pytest-xdist
- Wrap BibTeX examples in Jekyll raw blocks for docs build
- Fix thread-order-dependent assertion in client lifecycle test
- Expand Honcho docs: session isolation, lifecycle, routing internals

Dropped from original PR:
- Indentation change in _create_request_openai_client that would move
  client creation inside the lock (causes unnecessary contention)

Co-authored-by: adavyas <adavyas@users.noreply.github.com>

tests/test_openai_client_lifecycle.py

@@ -145,8 +145,9 @@ def test_concurrent_requests_do_not_break_each_other_when_one_client_closes(monk
     thread_one.join(timeout=5)
     thread_two.join(timeout=5)
 
-    assert isinstance(results["first"], APIConnectionError)
-    assert results["second"] == {"ok": "second"}
+    values = list(results.values())
+    assert sum(isinstance(value, APIConnectionError) for value in values) == 1
+    assert values.count({"ok": "second"}) == 1
     assert len(factory.calls) == 2