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/src/server/agent/provider-launch-config.test.ts

@@ -66,7 +66,7 @@ describe("applyProviderEnv", () => {
       },
     };
 
-    const env = applyProviderEnv(base, runtime, {});
+    const env = applyProviderEnv(base, runtime);
 
     expect(env.PATH).toBe("/usr/bin");
     expect(env.HOME).toBe("/custom/home");
@@ -74,21 +74,11 @@ describe("applyProviderEnv", () => {
     expect(Object.keys(env).length).toBeGreaterThanOrEqual(3);
   });
 
-  test("shell env PATH wins over base env PATH", () => {
-    const base = { PATH: "/usr/bin:/bin" };
-    const shellEnv = { PATH: "/usr/local/bin:/usr/bin:/bin:/home/user/.nvm/bin" };
-
-    const env = applyProviderEnv(base, undefined, shellEnv);
-
-    expect(env.PATH).toBe("/usr/local/bin:/usr/bin:/bin:/home/user/.nvm/bin");
-  });
-
-  test("runtimeSettings env wins over shell env", () => {
+  test("runtimeSettings env wins over base env", () => {
     const base = { PATH: "/usr/bin" };
-    const shellEnv = { PATH: "/usr/local/bin:/usr/bin" };
     const runtime: ProviderRuntimeSettings = { env: { PATH: "/custom/path" } };
 
-    const env = applyProviderEnv(base, runtime, shellEnv);
+    const env = applyProviderEnv(base, runtime);
 
     expect(env.PATH).toBe("/custom/path");
   });
@@ -103,7 +93,7 @@ describe("applyProviderEnv", () => {
       CLAUDE_CODE_ENABLE_SDK_FILE_CHECKPOINTING: "true",
     };
 
-    const env = applyProviderEnv(base, undefined, {});
+    const env = applyProviderEnv(base);
 
     expect(env.PATH).toBe("/usr/bin");
     expect(env.CLAUDECODE).toBeUndefined();