chore: add pre-commit config and update CI pipeline

- .pre-commit-config.yaml with standard Go hooks: gofmt, go vet,
  go mod tidy, plus trailing whitespace, end-of-file, yaml check,
  large file check, merge conflict check
- go vet runs as a local hook with ./... to work correctly with
  Go modules (the dnephin hook runs per-file which breaks)
- Woodpecker pre-commit pipeline updated to use almalinux9-gobuilder
  image with uvx pre-commit run --all-files
- Pre-commit hooks installed into the repo

.woodpecker/pre-commit.yaml

@@ -3,7 +3,15 @@ when:
 
 steps:
   - name: pre-commit
-    image: golang:1.25
+    image: git.unkin.net/unkin/almalinux9-gobuilder:20260606
     commands:
-      - test -z "$(gofmt -l .)"
-      - go vet ./...
+      - uvx pre-commit run --all-files
+    backend_options:
+      kubernetes:
+        resources:
+          requests:
+            memory: 512Mi
+            cpu: 1
+          limits:
+            memory: 2Gi
+            cpu: 2