fix(mir/builder): use function-local ValueId throughout MIR builder

Phase 25.1b: Complete SSA fix - eliminate all global ValueId usage in function contexts.

Root cause: ~75 locations throughout MIR builder were using global value
generator (self.value_gen.next()) instead of function-local allocator
(f.next_value_id()), causing SSA verification failures and runtime
"use of undefined value" errors.

Solution:
- Added next_value_id() helper that automatically chooses correct allocator
- Fixed 19 files with ~75 occurrences of ValueId allocation
- All function-context allocations now use function-local IDs

Files modified:
- src/mir/builder/utils.rs: Added next_value_id() helper, fixed 8 locations
- src/mir/builder/builder_calls.rs: 17 fixes
- src/mir/builder/ops.rs: 8 fixes
- src/mir/builder/stmts.rs: 7 fixes
- src/mir/builder/emission/constant.rs: 6 fixes
- src/mir/builder/rewrite/*.rs: 10 fixes
- + 13 other files

Verification:
- cargo build --release: SUCCESS
- Simple tests with NYASH_VM_VERIFY_MIR=1: Zero undefined errors
- Multi-parameter static methods: All working

Known remaining: ValueId(22) in Stage-B (separate issue to investigate)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

lang/src/llvm_ir/emit/LLVMEmitBox.hako

@@ -11,6 +11,8 @@
 // - Provider examples: ny-llvmc wrapper or llvmlite harness via a Plugin box `LLVMCodegenBox.emit_object/2`.
 // - This stub only validates inputs and reports provider availability via env.
 
+using selfhost.shared.host_bridge.codegen_bridge as CodegenBridgeBox
+
 static box LLVMEmitProviderBox {
   // Availability probe (for canaries)
   is_available() {
@@ -39,11 +41,10 @@ static box LLVMEmitProviderBox {
     }
     local pv = "" + p
     if pv == "ny-llvmc" {
-      local args = new ArrayBox(); args.push(mir_json)
       // env.codegen.emit_object(mir_json)
-      local ret = hostbridge.extern_invoke("env.codegen", "emit_object", args)
+      local ret = CodegenBridgeBox.emit_object(mir_json)
       return ret
- }
+   }
     if pv == "llvmlite" {
       // Not wired yet for llvmlite provider
       print("[llvmemit/skip] provider stub; implement llvmlite Plugin v2 call")