docs: correct stale server, permission, and theme documentation - #44

Summary

Corrects stale documentation found while reviewing main at 28b93cc:

• Removes the contradictory "server hosting is planned for v2 / not available" line; servers:process is implemented and documented.
• Adds the five implemented permissions missing from the API and extension permission lists: modpacks:install, resourcepacks:install, shaderpacks:install, screenshots:read, screenshots:write.
• Clarifies that directories under servers/ are shared across extensions; servers:manage can list/delete any valid server directory, not only ones created by the same extension.
• Documents the theme sanitizer's actual restrictions: url(), @font-face, quoted strings, and full-window overlays. Adds the current font-bundling limitation and notes that sanitization runs at install time.
• Fixes the server-manager spec's references to missing dist-extensions/ examples and aligns Fabric/any-jar fallback and error text with findServerJar.
• Updates the SDK docs to mark the TypeScript snippet as a trimmed example and point to the full declarations.
• Notes the CLI's Go 1.26.2 requirement and corrects the stale GetCSS comment.

Testing

• go test ./pkg/theme
• git diff --check

No behavior changes.

^{Need help on this PR? Tag @codesmith-bot with what you need.}