docs(windows): expand windows.md with kernel bootstrap, env inheritance, lock cleanup

[abdulazizFarhan]

Expands packages/coding-agent/docs/windows.md with the IPython kernel bootstrap workflow for Windows.

Added sections:

• One-shot Python kernel provisioning (PowerShell + Git Bash variants). Lists all 13 required packages — with tyro and dill called out as the easy ones to miss (Prime Agent's bootstrap only reports the first missing group per run).
• PowerShell user-level env var inheritance quirk. setx writes a user-level var, but PowerShell does NOT auto-inherit user-level vars into the process env (cmd does). The wrapper must explicitly copy them via [System.Environment]::SetEnvironmentVariable($name, $value, 'Process'). This is the most common silent failure for PowerShell-launched prime-agent sessions.
• Stale session-leases/*.lock cleanup. proper-lockfile uses directories as locks on Windows. If the previous prime-agent was killed, the .lock directory blocks the next resume with EPERM: rename *.lock.candidate-XXX → *.lock. Wrapper should clear locks whose owner.json PID is no longer running.
• Failure-mode diagnosis checklist for the four common 'kernel broken' symptoms (POSIX-only bootstrap path, missing package, stale lock, bootstrap-version drift).

Why docs-only: the kernel path fix itself is already in PR #825 (fix/windows-console-flicker). This PR makes the existing workaround discoverable and documents the PowerShell + lock gotchas that bit me during setup. Closes the documentation gap for #660.

Note

Expand Windows documentation with kernel bootstrap, env inheritance, and lock cleanup

Adds several new sections to windows.md covering the full Windows setup and troubleshooting workflow:

• Documents the Python kernel bootstrap: per-user uv-managed venv location, required packages, and one-shot provisioning commands for PowerShell and Git Bash
• Adds a PowerShell snippet to import user-level environment variables before launching prime-agent, addressing env inheritance gaps on Windows
• Provides a PowerShell script to clean up stale session-lease *.lock directories whose owning PID no longer exists
• Adds a failure-mode diagnosis section covering POSIX-only path bugs, missing packages under a custom Python override, stale lock rename errors, and out-of-sync .bootstrap-version

^{Macroscope summarized f366c91.}