feat(publish): wire sanitizer + output-first hero into orchestrator

[ucguy4u]

Summary

Closes the deferred follow-up from #5. Wires the publish sanitizer (already on main) into `Orchestrator.publish()` and adds an output-first hero image picker with terminal fallback.

Changes

`Orchestrator.publish()` now:

1. Sanitizes body — calls `sanitize_body_for_publish()` before `client.publish()`. JSON command manifest, exec-proof block, and screenshot plan sections never reach WP. No-op fast path when body is clean.
2. Output-first hero — prefers `output_.png` (command result) over `terminal_.png` (command line, duplicates body code block).
3. Resilient fallback — if output upload raises `PublishError`, retries with terminal so a bad output proof never publishes a hero-less post.

Implementation notes

• Single `iterdir()` partition replaces two glob calls (TOCTOU race fixed per codex review).
• Body `model_copy` only fires when sanitizer mutates content.

Tests added (6)

test	purpose
`strips_scaffolding_from_body_before_wp_call`	sanitizer called, scaffolding gone from passed body
`clean_body_skips_body_model_copy`	sanitizer called once with original body, no spurious mutation
`dirty_body_triggers_model_copy`	sanitized body reaches `wp.publish`
`prefers_output_screenshot_as_hero`	output picked over terminal when both present
`falls_back_to_terminal_when_no_output_image`	terminal used when no output
`falls_back_to_terminal_when_output_upload_fails`	resilience: retry terminal on output upload error

`WordPressClient` mock spec'd so signature drift fails fast.

Test plan

• `pytest tests/test_orchestrator.py tests/test_publish_sanitizer.py` — all green
• Full suite: 657 passed
• Codex review (4 findings addressed: fallback regression, idempotency proof, glob race, unspec'd mock)
• After merge: end-to-end `brewpress approve-publish` against staging WP confirms sanitized body reaches WP

Out of scope

Sandbox skip-empty-output rule (`sandbox_tutorial_media.py`) is independent and lands with the sandbox track.

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