chore: replace all node/npm/tsx references with bun across codebase

- Source: setup/service.ts, runners.ts, agent-runner.ts error messages
- Scripts: restart-stack.sh, run-migrations.ts → bun
- Bootstrap: setup.sh check_node→check_bun, npm install→bun install
- Docs: CLAUDE.md, README.md, all SKILL.md files
- Tests: service.test.ts, restart-stack.test.ts expectations updated

setup/service.test.ts

@@ -149,13 +149,13 @@ describe('systemd unit generation', () => {
 
   it('sets correct ExecStart', () => {
     const unit = generateSystemdUnit(
-      '/usr/bin/node',
+      '/usr/bin/bun',
       '/srv/ejclaw',
       '/home/user',
       false,
     );
     expect(unit).toContain(
-      'ExecStart=/usr/bin/node /srv/ejclaw/dist/index.js',
+      'ExecStart=/usr/bin/bun /srv/ejclaw/dist/index.js',
     );
   });
 });
@@ -207,7 +207,7 @@ describe('service definitions', () => {
   it('generates a oneshot stack restart unit', () => {
     const unit = buildStackRestartSystemdUnit(
       '/srv/ejclaw',
-      '/usr/bin/node',
+      '/usr/bin/bun',
       '/home/user',
     );