chore: modernize CI and update Go toolchain

- Bump Go from 1.19 to 1.26 and update all dependencies
- Rewrite CI workflow with matrix strategy (Linux, macOS, Windows)
- Update GitHub Actions to current versions (checkout@v4, setup-go@v5)
- Update CodeQL actions from v1 to v3
- Fix cross-platform bug in mock/path.go (path.Join -> filepath.Join)
- Clean up dependabot config (weekly schedule, remove stale ignore)

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

vendor/github.com/alecthomas/chroma/v2/lexers/embedded/ini.xml

@@ -9,6 +9,13 @@
     <filename>*.inf</filename>
     <filename>*.service</filename>
     <filename>*.socket</filename>
+    <filename>*.container</filename>
+    <filename>*.network</filename>
+    <filename>*.build</filename>
+    <filename>*.pod</filename>
+    <filename>*.kube</filename>
+    <filename>*.volume</filename>
+    <filename>*.image</filename>
     <filename>.gitconfig</filename>
     <filename>.editorconfig</filename>
     <filename>pylintrc</filename>
@@ -42,4 +49,4 @@
       </rule>
     </state>
   </rules>
-</lexer>
+</lexer>