fix: support map and set at global scope

[cs01]

Summary

• Global-scope Map<string, *> and Set<string> now work instead of erroring with "wrap in a function"
• Root cause: global variables use pointer-to-pointer indirection (@m is %StringMap**, not %StringMap*). Method dispatch and variable expression generation passed the raw global address to map/set operations that expected a direct struct pointer.
• Fixed in 3 places: variables.ts (expression generation loads through global pointer), method-calls.ts (map/set method dispatch loads through global pointer), llvm-generator.ts (restored global map declaration with proper metadata)

Test plan

• New test: map-global-scope.ts — global map set/get/has/size
• New test: set-global-scope.ts — global set add/has/size
• All 464 tests pass
• Self-hosting verification passes (Stage 0 + Stage 1)

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