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>

functions/__auto_source_fallback_venv.fish

@@ -0,0 +1,27 @@
+# Copyright (C) 2026 Rootiest
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+function __auto_source_fallback_venv --on-variable PWD
+    status --is-command-substitution; and return
+    
+    # 1. Skip if direnv is already managing this directory
+    if set -q DIRENV_DIR; or test -e ".envrc"
+        return
+    end
+    
+    # 2. If we are already in a venv, check if we've left its tree
+        if set -q VIRTUAL_ENV
+                # Check if the current PWD is still within the directory that owns the venv
+                # (Assuming the venv is at the root of the project)
+                set -l venv_root (string replace -r '/.venv$' '' $VIRTUAL_ENV)
+                if not string match -q "$venv_root*" "$PWD"
+                        type -q deactivate; and deactivate
+                end
+                return
+        end
+    
+        # 3. Only source the venv if we aren't already in one
+    if test -e ".venv/bin/activate.fish"
+        source .venv/bin/activate.fish
+    end
+end