feat(config): refactor config.fish, add XDG compliance, new functions, and keybindings

Restructure and expand the Fish shell configuration for better XDG compliance,
interactive-session gating, modularity, and ergonomics.

config.fish:
- Add full XDG Base Directory variable block (XDG_CONFIG_HOME, XDG_CACHE_HOME,
  XDG_DATA_HOME, XDG_STATE_HOME) and redirect tool caches/configs accordingly
  (cargo, rustup, go, bun, npm, gnupg, wakatime, wget, nvidia, codeium, etc.)
- Add editor setup with `type -q nvim` guard and NVIM_APPNAME
- Add CDPATH block (., ~/projects, ~) with explanatory comments
- Gate all interactive-only setup (key bindings, FZF, direnv, starship, secrets,
  local overrides, CLAUDE_CODE_NO_FLICKER) behind `status is-interactive`
- Guard FZF integration source behind a file-existence check
- Move secrets.fish and local.fish sourcing into the interactive block as overrides
- Remove obsolete universal `cdp` variable and duplicate PATH/editor blocks
- Update PATH entries to use XDG-resolved $CARGO_HOME and $BUN_INSTALL

conf.d/theme.fish:
- Move FZF_DEFAULT_OPTS (Catppuccin Mocha palette) from config.fish into theme.fish
  so all theming lives in one place
- Add section header for FZF colors; condense file header comment

conf.d/abbr.fish:
- Add `/exit` abbreviation as a vim-style alias for the `exit` builtin

conf.d/key_bindings.fish:
- Bind Ctrl+Alt+= to new `qalc_eval` function (inline Qalculate! evaluation)
- Add binding in both normal and all Vi modes
- Add descriptive comment block explaining the keybinding purpose

functions/bash.fish:
- Pass `--rcfile "$XDG_CONFIG_HOME/bash/bashrc"` so bash respects XDG config location

functions/cat.fish:
- Extend cat wrapper: detect directory arguments and delegate to `ls` instead of bat
- Preserve stdin-passthrough behavior when no arguments are provided

functions/__auto_source_fallback_venv.fish (new):
- Extract auto-venv PWD watcher from config.fish into its own autoloaded function file
- Skips activation when direnv manages the directory (.envrc present or DIRENV_DIR set)
- Deactivates venv when leaving its project tree

functions/ld.fish (new):
- Wrapper for lazydocker that injects the active Docker context's DOCKER_HOST,
  enabling correct context-aware operation

functions/joplin.fish (new):
- Joplin CLI wrapper function

functions/qalc_eval.fish (new):
- Inline Qalculate! evaluator: reads the current commandline buffer, passes it to
  `qalc`, prints the result, and clears the buffer for rapid-fire math in the shell

README.md:
- Remove stale `cdp` variable example from the local.fish documentation section

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

conf.d/theme.fish

@@ -4,10 +4,9 @@
 #          ╭──────────────────────────────────────────────────────────╮
 #          │                       Fish Theme                         │
 #          ╰──────────────────────────────────────────────────────────╯
-#
-# Catppuccin Mocha syntax highlighting colors.
-# These variables were migrated from the universal scope to global scope.
+# Catppuccin Mocha
 
+#   ────────────────────── Syntax highlighting colors ──────────────────────
 set --global fish_color_autosuggestion 6c7086
 set --global fish_color_cancel f38ba8
 set --global fish_color_command 89b4fa
@@ -47,3 +46,11 @@ set --global fish_pager_color_selected_background
 set --global fish_pager_color_selected_completion
 set --global fish_pager_color_selected_description
 set --global fish_pager_color_selected_prefix
+
+#   ─────────────────────────── FZF theme colors ───────────────────────────
+set -Ux FZF_DEFAULT_OPTS "\
+--color=bg+:#313244,bg:#1E1E2E,spinner:#F5E0DC,hl:#F38BA8 \
+--color=fg:#CDD6F4,header:#F38BA8,info:#CBA6F7,pointer:#F5E0DC \
+--color=marker:#B4BEFE,fg+:#CDD6F4,prompt:#CBA6F7,hl+:#F38BA8 \
+--color=selected-bg:#45475A \
+--color=border:#6C7086,label:#CDD6F4"