feat: add commit-helper tool to optimize AI commit context

Replaces verbose git command invocations in commit commands with a smart
TypeScript helper that:
- Filters out lockfiles, binary files, and generated content from diffs
- Truncates large diffs intelligently by preserving complete file changes
- Provides structured summaries with file type distribution and change stats
- Shows previews of new files being added

Also adds Fish shell VSCode extension and enables Claude Code panel preference.

.vscode/extensions.json

@@ -1,5 +1,6 @@
 {
     "recommendations": [
-        "thenuprojectcontributors.vscode-nushell-lang"
+        "thenuprojectcontributors.vscode-nushell-lang",
+        "bmalehorn.vscode-fish"
     ]
 }