fix(desktop): resolve login shell environment at Electron startup

On macOS, apps launched from Finder/Dock inherit a minimal environment
(PATH is just /usr/bin:/bin:/usr/sbin:/sbin). This caused two problems:
1. Agent binaries like codex were not detected (findExecutable failed)
2. Terminals spawned by Paseo had no access to user-installed tools
   (node, bun, direnv — all "command not found")

Fix: at Electron startup, spawn the user's login shell and capture its
full environment via JSON.stringify(process.env) using UUID markers.
This is the same battle-tested approach VS Code uses. The resolved
environment is merged into process.env before the daemon starts, so
all child processes — agents, terminals, git operations — inherit the
correct environment automatically.

This replaces the previous approach of invoking resolveShellEnv() (via
the shell-env npm package) at multiple scattered call sites. Now there
is a single source of truth: process.env is enriched once at startup.

Changes:
- New: packages/desktop/src/login-shell-env.ts (VS Code approach)
- Removed: resolveShellEnv(), shell-env dependency, $SHELL -lic probes
- Simplified: applyProviderEnv() and findExecutable() now trust process.env

packages/server/package.json

@@ -86,7 +86,6 @@
     "pino-pretty": "^13.1.3",
     "qrcode": "^1.5.4",
     "rotating-file-stream": "^3.2.9",
-    "shell-env": "^4.0.3",
     "sherpa-onnx": "1.12.28",
     "sherpa-onnx-node": "1.12.28",
     "strip-ansi": "^7.1.2",