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/key_bindings.fish

@@ -36,6 +36,14 @@
 # If the current command text is empty, the previous command's first token will be used instead.
 # ──────────────────────────────────────────────────────────────────────
 
+# ────────────── Bind Quick Qalc Evaluation to Ctrl+Alt+= ──────────────
+# Passes the current command line buffer to the Qalculate! CLI (qalc)
+#
+# Example: If you type `150 * 1.08` and press Ctrl+Alt+=, 
+# it will print the result (162) and clear the command line.
+# This allows for rapid-fire math without leaving the current shell.
+# ──────────────────────────────────────────────────────────────────────
+
 function fish_user_key_bindings
 
     #   ───────────────────────────── Set Bindings ─────────────────────────────
@@ -44,6 +52,7 @@ function fish_user_key_bindings
     bind ctrl-g __insert_previous_path_head
     bind ctrl-f __interactive_history_sub
     bind ctrl-alt-u _replace_command_token
+    bind ctrl-alt-= qalc_eval
 
     # Set bindings for all Vi modes:
     # 'default' is Vi-Command, 'insert' is Vi-Insert, 'visual' is Vi-Visual
@@ -51,5 +60,6 @@ function fish_user_key_bindings
         bind --mode $mode ctrl-g __insert_previous_path_head
         bind --mode $mode ctrl-f __interactive_history_sub
         bind --mode $mode ctrl-alt-u _replace_command_token
+        bind --mode $mode ctrl-alt-= qalc_eval
     end
 end