feat(languages): support static injections and scalable pack validation

[fcoury-oai]

Arborium-backed language packs commonly describe embedded languages with static Tree-sitter query properties, but Red previously recognized only dynamic language captures. Red also rebuilt and revalidated the entire language registry after accepting every language definition, making startup and reload increasingly expensive as the pack catalog grows.

This change prepares the editor for independently installed Arborium-backed packs:

• Honor (#set! injection.language "...") while preserving existing dynamic captures and giving explicitly configured static languages deterministic precedence.
• Keep injected languages optional: missing grammars are skipped, and opening one pack never installs or approves another pack.
• Validate language definitions incrementally so previously accepted native grammars are not reopened, rehashed, and recompiled for every subsequent definition.
• Preserve per-language quarantine: a broken definition does not remove earlier or later valid languages.
• Update language-pack documentation and the distribution decision to reflect the existing catalog, independent package lifecycle, and source-only Arborium architecture.

Companion language-pack importer: codersauce/red-language-packs#1.

How to Test

1. Run cargo test --lib highlighter::tests::static_injection_properties_highlight_available_nested_source and confirm statically selected JavaScript receives syntax highlighting inside Markdown.
2. Run cargo test --lib highlighter::tests::dynamic_tree_sitter_injection_captures_remain_supported and confirm existing dynamically selected fenced languages remain unchanged.
3. Run cargo test --lib language::tests::invalid_language_does_not_remove_previously_or_subsequently_accepted_languages and confirm only the invalid definition is quarantined.
4. Install the companion Go and Swift packs with explicit --trust-native-grammars, then run red --check-config; both independent languages should load successfully.
5. Install a pack in a fresh configuration without --trust-native-grammars, then run red --check-config; expect CFG401 and an explicit native-grammar approval requirement.

[fcoury-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Breezy!

Reviewed commit: 049cf212c4

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