Rename fastfetch.nix -> settings/shell.nix, remove flatpaks

- Move shell/prompt/font config from apps/fastfetch.nix to settings/shell.nix
- Remove flatpaks.nix and nix-flatpak flake input (no flatpak packages in use)
- Update readme structure and flake inputs table

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

settings/shell.nix

@@ -0,0 +1,130 @@
+{ config, pkgs, lib, ... }:
+{
+  # Install fastfetch
+  environment.systemPackages = with pkgs; [
+    fastfetch
+  ];
+
+  # Install Nerd Fonts for icon support
+  fonts.packages = with pkgs; [
+    nerd-fonts.fira-code
+    nerd-fonts.jetbrains-mono
+    nerd-fonts.meslo-lg
+  ];
+
+  # Simple fastfetch config — run `fastfetch` manually for system info
+  environment.etc."fastfetch/config.jsonc".text = ''
+    {
+      "$schema": "https://github.com/fastfetch-cli/fastfetch/raw/dev/doc/json_schema.json",
+      "logo": {
+        "source": "none"
+      },
+      "display": {
+        "separator": " ",
+        "color": {
+          "keys": "blue",
+          "title": "cyan"
+        },
+        "key": {
+          "type": "icon"
+        }
+      },
+      "modules": [
+        {
+          "type": "title",
+          "format": "{user-name}@{host-name}"
+        },
+        "separator",
+        "os",
+        "kernel",
+        "shell",
+        "terminal",
+        "uptime",
+        "memory"
+      ]
+    }
+  '';
+
+  # Fish shell settings and custom powerline prompt
+  programs.fish.interactiveShellInit = ''
+    # Disable default greeting
+    set -g fish_greeting
+
+    # Custom powerline prompt
+    function fish_prompt
+      set -l last_status $status
+
+      # Nix-shell indicator
+      if set -q IN_NIX_SHELL
+        set_color -o yellow
+        printf "[nix-shell] "
+        set_color normal
+      end
+
+      # --- Line 1: powerline segments ---
+      # Left round cap + NixOS icon
+      set_color 394b70
+      printf ""
+      set_color 7dcfff -b 394b70
+      printf "  "
+
+      # Arrow transition: nix -> hostname
+      set_color 394b70 -b e0af68
+      printf ""
+      set_color 1a1b26 -b e0af68
+      printf " %s " (hostname)
+
+      # Path segments - each folder gets its own color
+      set -l realhome (string escape --style=regex -- $HOME)
+      set -l rawpath (string replace -r "^$realhome" "~" $PWD)
+      set -l parts (string split "/" $rawpath)
+      set -l path_colors 41a6b5 9ece6a 7aa2f7
+
+      set -l prev_bg e0af68
+      set -l seg_count 0
+
+      for part in $parts
+        if test -n "$part"
+          set seg_count (math $seg_count + 1)
+          set -l cidx (math "(" $seg_count - 1 ")" "%" 3 + 1)
+          set -l seg_bg $path_colors[$cidx]
+
+          # Arrow from previous segment
+          set_color $prev_bg -b $seg_bg
+          printf ""
+          set_color 1a1b26 -b $seg_bg
+          printf " %s " $part
+
+          set prev_bg $seg_bg
+        end
+      end
+
+      # Git branch (if in a repo)
+      set -l branch (command git branch --show-current 2>/dev/null)
+      if test -n "$branch"
+        set_color $prev_bg -b bb9af7
+        printf ""
+        set_color 1a1b26 -b bb9af7
+        printf "  %s " $branch
+        set prev_bg bb9af7
+      end
+
+      # Final arrow to terminal bg
+      set_color $prev_bg -b normal
+      printf ""
+      set_color normal
+      printf "\n"
+
+      # --- Line 2: prompt character ---
+      if test $last_status -ne 0
+        set_color red
+      else
+        set_color magenta
+      end
+      printf "❯ "
+      set_color normal
+    end
+
+    function fish_right_prompt; end
+  '';
+}