Rename plain-lint skill to plain-fix

The name now matches the primary command (plain fix) and is action-oriented.
- /fix = quick code cleanup during development
- /pre-commit = comprehensive validation when done

Author: davegaeddert

plain-code/plain/code/skills/plain-fix/SKILL.md

@@ -0,0 +1,25 @@
+---
+name: plain-fix
+description: Fixes code formatting and linting issues. Use during development to clean up code as you work.
+---
+
+# Fix Code Issues
+
+```
+uv run plain fix [path]
+```
+
+Automatically fixes formatting and linting issues using ruff and biome.
+
+Options:
+
+- `--unsafe-fixes` - Apply ruff unsafe fixes
+- `--add-noqa` - Add noqa comments to suppress errors
+
+## Check Without Fixing
+
+```
+uv run plain code check [path]
+```
+
+Runs ruff, ty (type checking), biome, and annotation coverage checks without auto-fixing.