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

[conorbronsdon]

Rolls the quick-win templates proven on mojo-xml and mojo-feed across this repo:

• Canonical format commit: mojo format output committed as its own commit (touches the generated tables.mojo too — formatting only, conformance still 20034/20034).
• Format gate in CI: test workflow now fails if sources aren't mojo format-clean (pixi run fmt to fix locally).
• API-doc site: docs/render_api.py + docs.yaml workflow render mojo doc JSON to a static HTML API reference (pixi run docs locally).
• recipe.yaml: rattler-build recipe distributing the pure-Mojo source tree with a runtime mojo pin (same rationale as mojo-xml's recipe — no .mojopkg ABI lock-in).
• bench/: bench_normalize.mojo decodes the vendored NormalizationTest corpus into real Unicode text and reports MB/s for NFC/NFD/NFKC/NFKD (pixi run bench, local-only, not in CI).
• Capitalized the package docstring summary so mojo doc emits no warnings.

Verified locally: unit tests 24/24, conformance 20034/20034, docs render, bench compiles and runs, format-gate simulation passes.

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