call hierarchy (incoming/outgoing calls)

[michaeldistel]

Summary

Implement textDocument/prepareCallHierarchy and callHierarchy/incomingCalls / callHierarchy/outgoingCalls to show call trees for functions and FBs.

Scope

• Prepare: identify FUNCTION or FUNCTION_BLOCK under cursor as hierarchy root
• Incoming: all PROGRAM/FUNCTION_BLOCK/FUNCTION bodies that call this function/FB
• Outgoing: all functions/FBs called from the current PROGRAM/FUNCTION_BLOCK/FUNCTION
• Cross-file via workspace indexer

Implementation Notes

• New CallHierarchyProvider in src/server/providers/
• Requires workspace indexer to track call sites per file
• Register capability in server.ts

Acceptance

• Right-click → Show Call Hierarchy works on any FUNCTION or FUNCTION_BLOCK
• Incoming and outgoing populated correctly cross-file
• Tests cover direct and transitive call cases