linked editing for paired keywords

[michaeldistel]

Summary

Implement textDocument/linkedEditingRange so that renaming a PROGRAM, FUNCTION_BLOCK, or FUNCTION declaration name simultaneously updates the paired closing keyword.

Scope

• Paired keywords: FUNCTION_BLOCK / END_FUNCTION_BLOCK, FUNCTION / END_FUNCTION, PROGRAM / END_PROGRAM
• Editing the name after the opening keyword updates the trailing comment or paired identifier if present

Implementation Notes

• New LinkedEditingProvider in src/server/providers/
• Register linkedEditingRangeProvider capability in server.ts

Acceptance

• Editing the name in an opening keyword reflects in the closing label (if used)
• Does not fire in comments or strings
• Tests cover PROGRAM, FUNCTION_BLOCK, and FUNCTION