fix module-scope variables defaulting to double instead of actual type

[cs01]

Summary

Fix module-scope variables defaulting to double instead of their actual type, causing LLVM opt crashes.

Problem

Top-level variable declarations like const parts = "hello".match(/re/) crashed during LLVM optimization with type mismatches:

'%1' defined with type 'ptr' but expected 'double'

The same code worked fine when wrapped in a function.

Root cause

Module-scope variables go through a two-phase process:

1. generateGlobalVariableDeclarations() emits @name = global <type> <default>
2. allocate() in @main stores the expression result into the pre-declared global

Phase 1 has an incomplete type classifier (~12 cases) compared to the function-local path which handles 25 cases via classifyVariable(). When it couldn't determine the type, it fell back to double — so .match(), .split(), function calls returning strings, etc. all became @name = global double 0.0. Phase 2 then tried to store i8* %expr, double* @name, causing the type mismatch.

Additionally, struct-value globals (%StringArray, %Array, %Map, %Set) were declared as by-value structs with zeroinitializer, while the function-local path correctly uses pointer types — another source of mismatches.

Fix

• Convert all struct-value global types to pointer types matching the local path (%StringArray -> %StringArray*, %Array -> %Array*, %Map -> %Map*, etc.)
• Extend the global store path to bitcast when the expression's actual type doesn't match the global's declared pointer type
• Remove the now-unnecessary struct-value load+store branch
• Replace the silent double fallback with a compile error for unclassified expression types — instead of silently guessing the wrong type and crashing later in opt, the compiler now tells you: cannot determine type of module-scope variable 'x'. Move the declaration inside a function, or add a type annotation
• Number literals (const x = 42) still correctly default to double

Test plan

• Added 3 test fixtures in tests/fixtures/globals/ (module-scope .match(), .split(), function return)
• All 355 tests pass (native compiler)
• All 222 tests pass (Node.js compiler)