ci: implement Promise.all semantics for parallel typecheck and web build with fail-fast behavior

Replace shell-based parallel execution with bun runtime Promise.all implementation:
- Use child_process.spawn wrapped in Promises for better error handling
- Implement fail-fast behavior where any command failure immediately exits
- Maintain parallel execution of typecheck and web build commands
- Add clear success/failure messaging with emoji indicators
- Leverage bun's JavaScript runtime for more robust process orchestration

This improves CI reliability by ensuring proper error propagation and
cleaner failure modes compared to the previous shell-based approach.

Codebuff

Author: brandonkachen

.github/workflows/ci.yml

@@ -53,12 +53,21 @@ jobs:
 
       - name: Typecheck and Build web in parallel
         run: |
-          set -e
-          bun run typecheck &
-          PID1=$!
-          cd web && bun run build &
-          PID2=$!
-          wait $PID1 && wait $PID2
+          bun -e "
+          const { spawn } = require('child_process');
+          function runCommand(command, args, options = {}) {
+            return new Promise((resolve, reject) => {
+              const child = spawn(command, args, { stdio: 'inherit', ...options });
+              child.on('close', (code) => code === 0 ? resolve() : reject(new Error('Command failed with exit code ' + code)));
+              child.on('error', reject);
+            });
+          }
+          Promise.all([
+            runCommand('bun', ['run', 'typecheck']),
+            runCommand('bun', ['run', 'build'], { cwd: 'web' })
+          ]).then(() => console.log('✅ Both typecheck and web build completed successfully!'))
+          .catch(error => { console.error('❌ One or more commands failed:', error.message); process.exit(1); });
+          "
 
       # - name: Build npm-app
       #   run: cd npm-app && bun run build