Add path filters to CI and build workflows

Prevents workflows from running on changes to docs, README, infra,
summary.md, or other non-code files. Build workflow also skips on
test-only changes since tests don't affect the Docker image.

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

.forgejo/workflows/ci.yml

@@ -4,7 +4,19 @@ name: CI
 
 on:
   push:
+    paths:
+      - "src/**"
+      - "frontend/**"
+      - "tests/**"
+      - "pyproject.toml"
+      - ".forgejo/workflows/ci.yml"
   pull_request:
+    paths:
+      - "src/**"
+      - "frontend/**"
+      - "tests/**"
+      - "pyproject.toml"
+      - ".forgejo/workflows/ci.yml"
 
 jobs:
   typecheck: