fix(codex): preserve local environment hydration

[huntharo]

Summary

Preserve the local Codex environment setup result so future local Codex App Server threads can run with the same toolchain context instead of rediscovering nvm, pnpm, Corepack, and related PATH state on every command.

Changes

• Capture a filtered post-setup shell environment after successful local .codex/environments/*.toml setup.
• Persist the non-secret toolchain environment in the active PwrAgent profile state so it survives app restarts.
• Reuse cached hydration when setup is disabled or skipped.
• Pass the hydrated env to local Codex thread/start through config.shell_environment_policy.set.
• Apply the hydrated env to local environment actions as well.
• Add focused coverage for capture/filtering, cache reuse, and Codex thread/start payload generation.

Root Cause

PwrAgent ran environment setup commands in a child shell, but the resulting shell state could not mutate the parent Electron process or the Codex App Server thread config. That left local Codex turns with only the default process/login shell environment, so tools installed through project-specific version managers could be missing.

Validation

• ./node_modules/.bin/tsc --noEmit -p apps/desktop/tsconfig.json
• ./node_modules/.bin/vitest run apps/desktop/src/main/__tests__/codex-environment-runtime.test.ts apps/desktop/src/main/__tests__/codex-client.test.ts
• git diff --check