feat: add catppuccin nim-style fallback fish_prompt

functions/fish_prompt.fish

@@ -0,0 +1,138 @@
+# Copyright (C) 2026 Rootiest
+# SPDX-License-Identifier: AGPL-3.0-or-later
+#
+# SYNOPSIS
+#   fish_prompt
+#
+# DESCRIPTION
+#   Catppuccin Mocha fallback prompt (nim-style, two-line). Active whenever
+#   the starship prompt is not available — either starship is not installed or
+#   C3 overrides are disabled. Has no external dependencies; uses only fish
+#   builtins (set_color, fish_git_prompt, prompt_pwd, prompt_hostname).
+#
+# RETURNS
+#   0  Always; outputs the prompt to stdout
+#
+# EXAMPLE
+#   # Rendered automatically by fish; not called directly.
+function fish_prompt
+    set -l last_status $status
+
+    # Catppuccin Mocha hex palette
+    set -l c_green  a6e3a1
+    set -l c_red    f38ba8
+    set -l c_yellow f9e2af
+    set -l c_text   cdd6f4
+    set -l c_blue   89b4fa
+    set -l c_teal   94e2d5
+    set -l c_pink   f5c2e7
+    set -l c_dim    6c7086
+    set -l c_mauve  cba6f7
+
+    # Line/connector color tracks last exit status; brackets stay bold green
+    set -l retc $c_green
+    test $last_status -ne 0; and set retc $c_red
+
+    # Enable upstream arrows in git prompt (↑/↓)
+    set -q __fish_git_prompt_showupstream
+    or set -g __fish_git_prompt_showupstream auto
+
+    # ─── First line ───────────────────────────────────────────────────────────
+    set_color $retc
+    echo -n '┬─'
+    set_color --bold $c_green
+    echo -n '['
+
+    # Username: red if root, yellow otherwise
+    if functions -q fish_is_root_user; and fish_is_root_user
+        set_color --bold $c_red
+    else
+        set_color --bold $c_yellow
+    end
+    echo -n $USER
+
+    set_color --bold $c_text
+    echo -n '@'
+
+    # Hostname: teal if SSH, blue if local
+    if test -n "$SSH_CLIENT"
+        set_color --bold $c_teal
+    else
+        set_color --bold $c_blue
+    end
+    echo -n (prompt_hostname)
+
+    set_color --bold $c_text
+    echo -n ':'
+    set_color $c_text
+    echo -n (prompt_pwd)
+    set_color --bold $c_green
+    echo -n ']'
+    set_color normal
+
+    # Vi-mode segment ─[N/I/R/V]
+    if test "$fish_key_bindings" = fish_vi_key_bindings
+        or test "$fish_key_bindings" = fish_hybrid_key_bindings
+        set -l mode_str
+        switch $fish_bind_mode
+            case default
+                set mode_str (set_color --bold $c_red)'N'(set_color normal)
+            case insert
+                set mode_str (set_color --bold $c_green)'I'(set_color normal)
+            case replace_one replace
+                set mode_str (set_color --bold $c_teal)'R'(set_color normal)
+            case visual
+                set mode_str (set_color --bold $c_mauve)'V'(set_color normal)
+        end
+        set_color $retc
+        echo -n '─'
+        set_color --bold $c_green
+        echo -n '['
+        echo -n $mode_str
+        set_color --bold $c_green
+        echo -n ']'
+        set_color normal
+    end
+
+    # Virtual environment segment ─[V:name]
+    set -q VIRTUAL_ENV_DISABLE_PROMPT
+    or set -g VIRTUAL_ENV_DISABLE_PROMPT true
+    if set -q VIRTUAL_ENV
+        set_color $retc
+        echo -n '─'
+        set_color --bold $c_green
+        echo -n '['
+        set_color normal
+        set_color $retc
+        echo -n 'V:'(path basename "$VIRTUAL_ENV")
+        set_color --bold $c_green
+        echo -n ']'
+        set_color normal
+    end
+
+    # Git branch in Catppuccin Pink, wrapped in parens: (main)
+    set -l git_info (fish_git_prompt '%s')
+    if test -n "$git_info"
+        echo -n ' '
+        set_color $c_pink
+        echo -n "($git_info)"
+        set_color normal
+    end
+
+    echo  # newline
+
+    # Background jobs (one per line, dim)
+    for job in (jobs)
+        set_color $retc
+        echo -n '│ '
+        set_color $c_dim
+        echo $job
+    end
+
+    # ─── Second line ──────────────────────────────────────────────────────────
+    set_color $retc
+    echo -n '╰─>'
+    set_color --bold $c_red
+    echo -n '$ '
+    set_color normal
+end