ci: Add shallow git clone (depth: 1)

Only fetch latest commit instead of full history.
Reduces checkout time and bandwidth.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.woodpecker.yml

@@ -1,3 +1,8 @@
+# Shallow clone - only fetch latest commit (faster checkout)
+clone:
+  git:
+    depth: 1
+
 steps:
   # ===========================================
   # PR VALIDATION: Parallel type checks (PRs only)