feat(claude): add fish-validate and lua-format skills

Add fish-validate skill for syntax checking and formatting .fish files,
lua-format skill for stylua formatting, and fish_indent PostToolUse hook.

.claude/skills/lua-format/SKILL.md

@@ -0,0 +1,22 @@
+---
+name: lua-format
+description: >-
+  Format Lua files after editing.
+  Apply when writing or modifying any .lua file.
+user-invocable: false
+allowed-tools: Bash
+---
+
+After editing any `.lua` file, format it with stylua:
+
+```bash
+stylua <file>
+```
+
+Project settings are in `stylua.toml` (90-char line length).
+
+If stylua is not available, skip formatting silently.
+
+## Files to never format
+
+- Files inside `config/nvim/` managed by plugins (lazy.nvim lockfile)