canonical type resolver, handler dispatch, file-scoped mangling

[cs01]

Architecture improvements: canonical type resolver, handler dispatch, file-scoped mangling

Summary

Three independent improvements to the codegen infrastructure:

1. Canonical type resolver — Replace 8+ divergent TS-to-LLVM type mapping functions with one canonicalTypeToLlvm function. Fix paramIsInterface being hardcoded to false at call sites and getClassType returning i32* instead of i8*.

2. Handler dispatch refactor — Extract the generate() method's dispatch logic into a separate dispatchHandlers() method with documented priority ordering.

3. File-scoped function mangling — Add sourceFile to FunctionNode/ClassNode AST nodes. Non-exported functions in multi-file native compilation get file-scoped names (_cs_filename_func) to prevent cross-file collisions.

Changes

Shard 1: Canonical Type Resolver

• Add canonicalTypeToLlvm(tsType, mode, isEnum, isInterface, fieldName) to type-system.ts
• Rewrite tsTypeToLlvm, mapParamTypeToLLVM, mapReturnTypeToLLVM, tsTypeToLlvmJson as thin wrappers
• Fix paramIsInterface: false hardcoding in calls.ts (3 call sites) — now uses interfaceStructGenHasInterface()
• Fix getClassType() returning i32* instead of i8* in type-context.ts

Shard 2: Handler Dispatch

• Extract dispatch logic from generate() into dispatchHandlers() in member.ts
• Document handler priority ordering (15 handlers, priority 10-200)

Shard 3: File-Scoped Mangling

• Add sourceFile?: string to FunctionNode and ClassNode in ast/types.ts
• Set sourceFile in native parser (parser-native/transformer.ts)
• Build exportedNames: Set<string> from ast.exports in LLVMGenerator
• Update mangleUserName(name, sourceFile?) — non-exported functions get _cs_${fileSlug}_${name}
• Thread sourceFile through function-generator.ts and calls.ts

Known limitations

• Class constructors/methods in class.ts don't thread sourceFile yet
• TS parser doesn't set sourceFile (only matters for multi-file native compilation)
• Handler dispatch is still an if/else chain (Stage 0 can't do handlers[i](...))

Test plan

• TypeScript build passes
• All 299 unit tests pass (Node.js compiler)
• Self-hosting Stage 0 + Stage 1 + Stage 2 pass with smoke tests
• Native compiler test failures are pre-existing non-deterministic SIGSEGVs (same rate as main)