feat: initial fish shell configuration

- Core config layered on CachyOS base with Catppuccin Mocha theming
- Fisher plugins: fzf.fish, catppuccin, autopair, replay, puffer-fish, magic-enter, spark
- Smart CLI wrappers with fallbacks (bat, lsd, btop, dust, prettyping)
- Custom functions: git, docker, network, kitty, AI session management
- Extensive abbreviation system for keyboard-driven workflows
- Secrets/local sourcing pattern for private and machine-specific config
- README with full documentation and personalization guide
- AGPLv3+ license with copyright headers on all source files

functions/_autopair_backspace.fish

@@ -0,0 +1,9 @@
+function _autopair_backspace
+    set --local index (commandline --cursor)
+    set --local buffer (commandline)
+
+    test $index -ge 1 &&
+        contains -- (string sub --start=$index --length=2 -- "$buffer") $autopair_pairs &&
+        commandline --function delete-char
+    commandline --function backward-delete-char
+end