Add API-doc site, format gate, recipe.yaml, bench

[conorbronsdon]

Suite-wide quick wins, following the pattern established in mojo-xml and mojo-feed:

• Canonical formatting: committed mojo format output as its own commit, then added a format gate to the test workflow (mojo format + git diff --exit-code) so CI fails if sources drift from canonical format.
• API-doc site: docs/render_api.py (same renderer as mojo-xml) plus a docs.yaml workflow that builds mojo doc JSON into a static HTML API reference and deploys it to GitHub Pages.
• recipe.yaml: rattler-build recipe for eventual conda-channel publishing (ships the pure-Mojo source tree with a runtime mojo pin, not a compiled .mojopkg). Not wired to CI.
• bench/: small compiled benchmark timing urlparse/urlunparse round-trips and parse_qsl/urlencode round-trips over the CPython byte-match fixture corpus (test/data/fixtures.txt). Corpus is tiny, so it iterates 20k times for stable numbers. Local pixi run bench only, not in CI.
• pixi tasks: fmt, docs, bench added to pixi.toml; .gitignore extended for generated artifacts.
• Docstring lint: package docstring summary now starts with a capitalized word (mojo doc emits no summary warning).

Verified locally: pixi run test (38/38 pass, 173/173 fixture byte-match), pixi run docs, pixi run bench, and the format-gate simulation (pixi run fmt && git diff --exit-code) all pass.

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