smart expand selection (SelectionRange)

[michaeldistel]

Summary

Implement textDocument/selectionRange so Shift+Alt+Right progressively expands selection to enclosing AST nodes.

Scope

• Expression → statement → block body → PROGRAM/FUNCTION_BLOCK/FUNCTION body → full declaration
• Works in PROGRAM, FUNCTION_BLOCK, FUNCTION sections
• Registered in LSP server capabilities

Implementation Notes

• New SelectionRangeProvider in src/server/providers/
• Walks AST from cursor position outward
• Returns nested SelectionRange chain

Acceptance

• Expand selection grows through expression, statement, block, and full declaration correctly
• Shrink selection reverses
• Tests cover nested expressions and block boundaries