Add a Sphinx documentation site: MyST guides + autodoc API reference on Read the Docs

[roed-math]

A documentation site for psycodict: Sphinx + MyST-Parser + autodoc, furo theme, served on Read the Docs, with the build wired into CI so it can never silently rot.

Structure. The narrative guides are the existing root-level Markdown files — README (as "Getting started"), QueryLanguage, Searching, DataManagement, MetadataFormats — which docs/conf.py copies into docs/ at build time. That keeps the GitHub-rendered copies canonical (no duplication, no moved files, no broken deep links) while their relative links to one another turn into working site links. The API reference is one automodule page per module (all eleven), plus a hand-written map of how the pieces fit; the Sage-convention docstrings (INPUT:/OUTPUT: blocks, EXAMPLES:: transcripts, :meth:/:class: roles) are plain reST and render as-is. GitHub-style heading anchors are enabled so the guides' intra-page #links keep working; intersphinx links Python and psycopg references.

The build contract. A fifth CI job (docs, ~40s, no database — importing psycodict doesn't connect) runs sphinx-build -W --keep-going, and .readthedocs.yaml sets fail_on_warning to match: a broken cross-reference or malformed docstring fails the build rather than degrading the site. Getting to zero warnings surfaced eight real glitches, fixed in the first commit: over-/staircase-indented bullet continuations in the search/lucky INPUT blocks (docutils parses those as stray block quotes), an unterminated ``LISTEN``ed inline literal in NotificationListener, missing H1 titles in QueryLanguage.md and DataManagement.md (GitHub renders those better now too), and a Searching.md TOC link pointing at a raw <a name> anchor Markdown processors don't index (the anchor stays, so old deep links still work).

Build locally with:

pip install '.[pgbinary]' -r docs/requirements.txt
python -m sphinx -W --keep-going -b html docs docs/_build/html

One manual step to go live: import the repository at https://about.readthedocs.com (dashboard → Import a Project). From then on the RTD GitHub app builds every push and gives pull-request preview builds; once 1.0 is tagged, activate the tag under Versions so /stable/ serves the release while /latest/ tracks master.

Deliberately left to #113 (to avoid conflicts with the release capstone, which owns README and pyproject): adding Documentation = "https://psycodict.readthedocs.io" to [project.urls] and a docs badge to the README — one line each.

Future work (noted, not attempted here): the EXAMPLES:: blocks use sage: prompts and several still say from lmfdb import db — relics of the extraction, so they're illustrative rather than runnable. Rewriting them to >>> with psycodict-only setup would let them run as real doctests against the CI PostgreSQL service.

Verified: local build passes with zero warnings; ruff check . clean (conf.py included); built HTML spot-checked — furo assets, guide cross-links resolved to .html, the search/lucky parameter lists render as proper bullets, the notifications Forking/Hot standbys sections and the #parameters anchor all present.

🤖 Generated with Claude Code

[roed-math]

Review caught a cross-PR interaction with #123: it links Versioning.md from the README, but this site didn't copy or list it — the combined tree failed sphinx -W with myst.xref_missing on the README link (reproduced).

Fixed by stacking: versioning-policy is merged into this branch and Versioning.md is wired into _GUIDES, .gitignore and the toctree. Stacking (rather than just adding the wiring) keeps both merge orders green — wiring alone would make this PR's own docs build fail with FileNotFoundError until #123 landed, since conf.py copies every listed guide. If this merges first it simply brings #123's small content along, and #123 then merges as a no-op; if #123 merges first, the shared commit drops out of this diff.

Verified: combined build fails without the wiring, succeeds with it (sphinx -W --keep-going), Versioning.html is generated, the README link resolves to it, and Versioning.md's own links (QueryLanguage/Searching/DataManagement/MetadataFormats) all target guides already on the site.

[roed-math]

Follow-up: main also gained CONTRIBUTING.md and SECURITY.md, so they're now carried on the site too (own "Project" toctree caption). CONTRIBUTING.md links SECURITY.md + all four spec guides — all resolve on-site — and its Documentation section already documents this PR's sphinx -W build. Wiring them now also removes the next xref tripwire: a future "see CONTRIBUTING.md" line in any copied guide would have re-broken -W exactly like the Versioning.md link did. Build verified clean.