Add PR checks pipeline (fmt, clippy, test) and split CI config

- Split .woodpecker.yml into .woodpecker/check.yml (PR checks) and .woodpecker/deploy.yml (deploy on push to main)
- Add basic handler test to src/main.rs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.woodpecker/deploy.yml

@@ -0,0 +1,33 @@
+when:
+  - branch: main
+    event: push
+    path:
+      exclude:
+        - 'k8s/**'
+      on_empty: true
+
+steps:
+  - name: build-and-push
+    image: woodpeckerci/plugin-kaniko
+    settings:
+      registry: git.mikhailkilin.ru
+      repo: killingdruid/bcard
+      tags: ${CI_COMMIT_SHA}
+      username:
+        from_secret: docker_username
+      password:
+        from_secret: docker_password
+
+  - name: update-manifests
+    image: alpine/git
+    environment:
+      GIT_TOKEN:
+        from_secret: git_push_token
+    commands:
+      - 'printf "machine git.mikhailkilin.ru\nlogin killingdruid\npassword %s\n" "$GIT_TOKEN" > ~/.netrc'
+      - 'chmod 600 ~/.netrc'
+      - 'sed -i "s#image: git.mikhailkilin.ru/killingdruid/bcard:.*#image: git.mikhailkilin.ru/killingdruid/bcard:${CI_COMMIT_SHA}#" k8s/bcard.yaml'
+      - 'git config user.email "woodpecker@ci"'
+      - 'git config user.name "Woodpecker CI"'
+      - 'git add k8s/bcard.yaml'
+      - 'git diff --cached --quiet && echo "No changes" || (git commit -m "[CI SKIP] deploy ${CI_COMMIT_SHA}" && git push origin HEAD:main)'