Summary

Adds the Heart-owned reusable docs-build.yml workflow — the docs analogue of lib-tests.yml. The RTD hygiene census (PyAutoLabs/PyAutoFit#1341) found no PyAuto library builds its Sphinx docs pre-merge (ReadTheDocs runs fail_on_warning: false, no CI docs job anywhere), so broken API pages rot silently. Library repos call this thinly from .github/workflows/docs.yml; the build fails when the Sphinx warning count regresses past the repo's committed docs/sphinx_warning_baseline.txt (missing file = 0 = strict). Mechanics mirror lib-tests.yml: package→repo/deps mapping, sibling-branch-aware dependency clones, source installs with [optional,docs] extras.

Merge order: this PR merges FIRST — the PyAutoGalaxy/PyAutoLens caller PRs (PyAutoGalaxy#495-ish / PyAutoLens#597-ish, linked from #1341) reference docs-build.yml@main and their docs check errors until this lands.

API Changes

None — CI infrastructure only, no Python surface.

Test Plan

• PyAutoHeart suite: 244 passed (full, worktree)
• After merge: the Galaxy/Lens caller PRs' docs check goes green (Galaxy baseline 105, Lens 134, measured locally; if the CI count differs, recalibrate the baseline file once with justification — the job's error message documents this)

Validation checklist (--auto run)

• Effective level: supervised (header: supervised, cap: docs ≤ medium → safe)
• Plan: on the issue (docs: RTD hygiene — reconnect PyAutoFit RTD, converge conf.py, add docs CI PyAutoFit#1341), written at start; one disclosed scope rider (this repo added — CI idiom routes health checks through Heart)
• Gate: tests 244 pass (Heart) · smoke n/a (CI infra only, no script surface) · review CLEAN · Heart YELLOW within in-session ack at ship (4 pre-existing reasons listed on #1341)
• Human: plan sound in hindsight?
• Human: diff matches plan (no scope creep)?
• Human: merge, amend, or reject — then log the outcome

🤖 Generated with Claude Code

https://claude.ai/code/session_01GziFkivBHz1d11eFYUszmy