Align website with production Connect releases

[callumalpass]

Summary

• update desktop and CLI downloads from beta.46 to beta.54, the latest successfully published client release
• pin generated Connect documentation and schemas to beta.55, the exact production release commit
• update SDK documentation to beta.55 and replace the obsolete @mdbase/* package scope with the published @mdbase-dev/* scope
• refresh the version-pinned browser bundle URL and verified SHA-384 integrity value
• synchronize the production Connect schemas, problem catalog, query schema, file schema, operation catalog, theme roles, and conformance metadata

Release boundary

Production currently runs beta.55. Beta.56 is staged but has not been promoted, so this change does not link or recommend beta.56. Beta.55 did not produce a complete desktop GitHub release; beta.54 is therefore the newest production-compatible downloadable desktop/CLI release with a complete verified artifact set.

Validation

• pnpm test
• exact pinned specification import with MDBASE_SPEC_DIR=.sources/mdbase-spec pnpm import:spec
• pnpm check:links
• git diff --check
• verified beta.54 release contains all 35 expected assets
• recomputed the beta.55 browser bundle SHA-384 and matched the published integrity.json