Remove leftovers from the image-docs pipeline (#4102)

Cleanup after #4099, which made the AI docs bundle compile from this
repository alone. None of these changes alters what the build does.

## Changes

- **Drop the `httpx` pin** from `scripts/mcp-requirements.txt`. The pin
served the registry client that #4099 removed, and nothing imports
`httpx` now. `mcp` 2.2 depends on `httpx2`, a separate package, so the
pin only installed an unused library.
- **Delete `.github/workflows/templates/`.** Its three files were
blueprints for the images-private and courses exports to GCS, which
nothing reads anymore. Actions never ran them.
- **Rewrite `docs/automated-docs-setup.md`.** The guide still described
four sources, those templates, GCS downloads, and a local test that
needed placeholder sibling directories. It now covers the two sources,
the `scripts/` trigger, the package catalog, and a local test that runs
from a plain checkout.

## Deliberately not changed

The edu export's GCS upload and the compile workflow's `compiled/`
upload stay as they are. Neither has a known reader, but nobody can
check the bucket's access logs. DOCS-218, due 2026-10-28, revisits both,
once the 2026-09-30 MCP changes have settled and if ownership or readers
become known.

## Testing

- In a fresh virtual environment built from the new requirements,
`httpx` isn't installed, and `pytest scripts/test_mcp_server.py
scripts/test_mcp_transport.py scripts/test_compile_docs.py` passes (45
tests).
- Ran every command in the rewritten guide as written. The compile logs
`DFC mappings added`, and the catalog builds with 683 package mappings
and 397 image mappings.
- `grep` finds no remaining reference to `.github/workflows/templates/`.

Refs DOCS-138, DOCS-218

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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Created in collaboration with Claude Code running Opus 5.5 on
2026-09-30.

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Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

Author: matthewhelmke