v0.50.185: /btw stream hardening + .venv bootstrap + /reasoning toast (#935 #939 #941 #942)

* fix(bootstrap): discover .venv layout in agent_dir (closes #938) (#941)

* fix(btw): harden _streamDone flag — defensive ordering + session guard + stream_end coverage (#935)

* fix(btw): align /reasoning toast prefix with BRAIN const (#939)

* docs: v0.50.185 release notes, update test counts to 2107

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

bootstrap.py

@@ -113,7 +113,7 @@ def discover_launcher_python(agent_dir: Path | None) -> str:
     if env_python:
         return env_python
     if agent_dir:
-        for rel in ("venv/bin/python", "venv/Scripts/python.exe"):
+        for rel in ("venv/bin/python", "venv/Scripts/python.exe", ".venv/bin/python", ".venv/Scripts/python.exe"):
             candidate = agent_dir / rel
             if candidate.exists():
                 return str(candidate)