feat: untrusted workspace policy for binary execution

[SebTardif]

Problem

In untrusted workspaces (vscode.workspace.isTrusted === false), the extension currently discovers and executes binaries from PATH or user settings without restriction. A malicious workspace could include a patchloom binary that gets executed with the user's privileges.

Proposed Solution

When the workspace is untrusted:

1. Skip PATH discovery entirely
2. Ignore the patchloom.path setting (it could point to a workspace-relative path)
3. Only use the managed install binary (extension-controlled, verified checksum)
4. Show a warning if no managed install exists: "Patchloom CLI is not available in untrusted workspaces. Install via the managed installer or grant workspace trust."

Register a workspace trust handler:

vscode.workspace.onDidGrantWorkspaceTrust(() => {
  // Re-resolve binary with full discovery order
  refreshStatus();
});

Competitive Reference

astral-sh/ruff-vscode restricts to the bundled/managed binary in untrusted workspaces. This is a security best practice for any extension that executes external binaries.