Add automated installer with OS detection and curl pipe support

- install.sh: One-command installer with macOS/Ubuntu/Arch detection
  - Supports curl pipe (remote) and local execution
  - Interactive sudo prompt for Linux, user-level by default
  - Idempotent rc file edits with marker blocks
  - Backs up existing configs before overwriting
  - Installs: fonts, tmux, starship, fetch scripts, iTerm2 colors
  - --uninstall flag restores backups and removes all changes
- Update .gitignore to include fonts/ directory
- Update README.md with install instructions
- Update TERMINAL-SETUP.md to reference automated installer

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

README.md

@@ -21,9 +21,29 @@ Tokyo Night base with Aygea brand accent colors. Baby blue, sapphire, pink, silv
 
 See [TERMINAL-SETUP.md](TERMINAL-SETUP.md) for full step-by-step install instructions.
 
+## Install
+
+**One command:**
+```bash
+./install.sh
+```
+
+**Or remote (curl pipe):**
+```bash
+curl -fsSL https://raw.githubusercontent.com/itsaygea/aygeaNight/main/install.sh | bash
+```
+
+Flags: `--sudo` · `--skip-fonts` · `--skip-tmux` · `--skip-starship` · `--skip-fetch` · `--uninstall`
+
+The installer auto-detects your OS, installs all dependencies, and configures everything. It asks about sudo on Linux; defaults to user-level installs otherwise.
+
+See [TERMINAL-SETUP.md](TERMINAL-SETUP.md) for full step-by-step manual instructions.
+
+Run `./install.sh --help` for all options.
+
 ## Font
 
-This theme uses **JetBrainsMono Nerd Font**. It's not included in this repo — download it from [nerdfonts.com](https://www.nerdfonts.com/font-downloads).
+JetBrainsMono Nerd Font files are included in `fonts/JetBrainsMono/`. The installer copies them automatically.
 
 ## Colors