fix(claude-code-mcp): make run_mcp.sh bootstrap idempotent on Windows

[ottopichlhoefer]

Summary

• Resolves the venv interpreter via both bin/python and bin/python.exe. On Windows-built venvs the file is python.exe, and bash's [ -x ] test does not honor PATHEXT — so the previous probe never matched and the bootstrap branch fired on every session start.
• Splits venv creation from pip-sync. Pip now reruns only when the requirements cache is missing, requirements drifted, or mcp is not importable from the venv. Warm starts now skip both venv recreation and pip install, which also stops the cascade where re-running pip over the in-use venv hit ERROR_SHARING_VIOLATION on Windows and left orphan pip.exe/python3.exe processes locking the venv files.
• Aborts with a clear stderr message if venv creation still produces no usable interpreter, rather than failing later inside exec.

Fixes #1564.

Why

On Windows (msys2 bash + C:\msys64\mingw64\bin\python.exe), Claude Code logged Failed to reconnect to plugin:hindsight-memory:hindsight. at every session start. bash -x scripts/run_mcp.sh showed the bootstrap branch firing every time, falling back to python -m venv over an in-use venv, and erroring [Errno 13] Permission denied: '.../venv/bin/python3.exe'. Full reproduction in #1564.

Test plan

• bash -n hindsight-integrations/claude-code/scripts/run_mcp.sh — clean.
• Cold start (no venv): bootstrap creates the venv, pip installs, exec reaches mcp_server.py.
• Warm start (venv + cache present, mcp importable): both bootstrap probes short-circuit; script reaches exec without touching pip or recreating the venv. Verified on Windows 11 / msys2 5.2.37 / Python 3.12.11.
• Linux/macOS warm + cold smoke (would appreciate a CI check — I only have Windows handy).

Notes

• Behavior on systems where bin/python exists as an extensionless symlink (Linux/macOS) is unchanged: the first branch of resolve_py still hits.
• The script remains a single-file shell change; no Python/Node touched, so I skipped ./scripts/hooks/lint.sh.
• I'm not adding a tests/ entry — the existing pytest suite under hindsight-integrations/claude-code/tests/ covers Python modules, not the bootstrap shell. Happy to wire up a tiny shell-test harness if you want it.