fix(joinir): Phase 172 P0 - Remap PHI incoming Value IDs

Previously, PHI incoming values were not being remapped from JoinIR-local
ValueIds to Host ValueIds. Only the block IDs were remapped.

This fix ensures both block ID and value ID are remapped for PHI
instructions during JoinIR merge.

Note: trim still fails because condition variable exit values are not
being reflected in variable_map (Phase 172-4/5 work needed).

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

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

src/mir/builder/control_flow/joinir/merge/instruction_rewriter.rs

@@ -194,10 +194,13 @@ pub(super) fn merge_and_rewrite(
                         type_hint: None,
                     } => MirInstruction::Phi {
                         dst,
+                        // Phase 172: Fix P0 - Remap BOTH block ID AND value ID for PHI incoming
                         inputs: inputs
                             .iter()
                             .map(|(bb, val)| {
-                                (local_block_map.get(bb).copied().unwrap_or(*bb), *val)
+                                let remapped_bb = local_block_map.get(bb).copied().unwrap_or(*bb);
+                                let remapped_val = remapper.remap_value(*val);
+                                (remapped_bb, remapped_val)
                             })
                             .collect(),
                         type_hint: None,