ci(actions): add concurrency + path filter

- Add concurrency.cancel-in-progress to kill duplicate runs.
- Skip CI on **.md, docs/**, LICENSE changes.

Author: felixgeelhaar

.github/workflows/ci.yml

@@ -2,12 +2,24 @@ name: CI
 on:
   push:
     branches: [main]
+    paths-ignore:
+      - '**.md'
+      - 'docs/**'
+      - 'LICENSE'
   pull_request:
     branches: [main]
+    paths-ignore:
+      - '**.md'
+      - 'docs/**'
+      - 'LICENSE'
   schedule:
     # Weekly nox sweep — catches new CVEs in deps even when no commits land.
     - cron: '17 6 * * 1'
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 permissions:
   contents: read
   security-events: write