semantic token highlighting

[michaeldistel]

Summary

Implement textDocument/semanticTokens to provide richer, semantics-aware highlighting beyond what TextMate grammar can express.

Scope

• Token types: variable, function, functionBlock, type, parameter, keyword, operator, constant
• Token modifiers: declaration, definition, readonly, local, global
• Full, range, and delta variants
• Differentiate standard library vs user-defined symbols

Implementation Notes

• New SemanticTokensProvider in src/server/providers/
• Consume workspace indexer for symbol resolution
• Register capabilities in server.ts

Acceptance

• User-defined FBs highlighted differently from standard library FBs
• VAR_INPUT, VAR_OUTPUT, VAR_IN_OUT parameters visually distinct
• CONSTANT variables use readonly modifier
• Incremental delta updates on edits
• Tests cover token type and modifier assignments