chore(deps): bump .node-version to 26.12.1 (#28090)

Bump `.node-version` to 26.12.1.

- Node 24 moved to Maintenance LTS on 2026-10-20.
- Node 26 enters Active LTS on 2026-10-28.
- Includes the fixes from the [October 2026 security releases](https://nodejs.org/en/blog/vulnerability/october-2026-security-releases).
- Update the Node.js version in snapshots.

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

.node-version

@@ -1 +1 @@
-26.5.0
+26.12.1

crates/oxc_codegen/tests/integration/snapshots/stacktrace_is_correct.snap

@@ -1,7 +1,7 @@
 ---
 source: crates/oxc_codegen/tests/integration/sourcemap.rs
 ---
-Node.js version: v26.5.0
+Node.js version: v26.12.1
 
 ## Input
 const fn = () => {

tasks/transform_conformance/snapshots/babel_exec.snap.md

@@ -1,6 +1,6 @@
 commit: a56fe4a4
 
-node: v26.5.0
+node: v26.12.1
 
 Passed: 319 of 418 (76.32%)
 

tasks/transform_conformance/snapshots/oxc_exec.snap.md

@@ -1,6 +1,6 @@
 commit: a56fe4a4
 
-node: v26.5.0
+node: v26.12.1
 
 Passed: 40 of 42 (95.24%)