greenhouse_job_board_api: AI-optimize MCP action set

Greenhouse's Job Board API has no actions built in Pipedream today — there's nothing an agent can do with this integration yet. We'd like to build an initial action set so an agent can read job postings and submit applications, and so each tool is easy for an agent to configure.

A few things an agent can't do today, for example:
- List published job postings
- Get details for a specific job posting
- List departments and offices
- Submit a job application

**API reference:** https://developers.greenhouse.io/job-board.html

Note: this is Greenhouse's public Job Board API — distinct from the main recruiting/pipeline API.

**Add marker:**
When a component is AI-optimized, add this as the first line of the file:
```
// x-pd-ai: optimized
```
Add it to each action file and to the app's `.mjs` file.

Start by locating the greenhouse_job_board_api app's .mjs file and existing action-file structure, then read Greenhouse's Job Board API reference. Add actions for listing published jobs, getting a job's details, listing departments and offices, and submitting an application, with each action easy for an agent to configure. Add the x-pd-ai marker as the first line of every action file and the app's .mjs file.

Written by the indexing model from the issue text.