feat: add CLI with TUI, self-update, install script, and terminal section on landing page

- Full-screen Bubble Tea TUI with cream background fill using PadLine/FillBlankLines
- Self-update command (--update) pulling from GitHub releases
- install.sh for curl one-liner installation
- Terminal Lovers section on web landing page with install command and CLI features
- All 7 format categories, glob/directory batch support, auto-download ffmpeg

install.sh

@@ -0,0 +1,109 @@
+#!/bin/sh
+# Transmute CLI installer
+# Usage: curl -fsSL https://raw.githubusercontent.com/noauf/Transmute/main/install.sh | sh
+set -e
+
+REPO="noauf/Transmute"
+BINARY="transmute"
+INSTALL_DIR="/usr/local/bin"
+
+# Detect OS
+OS="$(uname -s)"
+case "$OS" in
+  Darwin)  OS="darwin" ;;
+  Linux)   OS="linux" ;;
+  MINGW*|MSYS*|CYGWIN*) OS="windows" ;;
+  *)
+    echo "Error: unsupported operating system: $OS"
+    exit 1
+    ;;
+esac
+
+# Detect architecture
+ARCH="$(uname -m)"
+case "$ARCH" in
+  x86_64|amd64) ARCH="x86_64" ;;
+  arm64|aarch64) ARCH="arm64" ;;
+  *)
+    echo "Error: unsupported architecture: $ARCH"
+    exit 1
+    ;;
+esac
+
+# Determine file extension
+if [ "$OS" = "windows" ]; then
+  EXT="zip"
+else
+  EXT="tar.gz"
+fi
+
+ASSET="${BINARY}-${OS}-${ARCH}.${EXT}"
+
+echo "Transmute CLI installer"
+echo "======================"
+echo ""
+echo "  OS:   $OS"
+echo "  Arch: $ARCH"
+echo ""
+
+# Get latest release tag
+echo "Fetching latest release..."
+TAG=$(curl -fsSL "https://api.github.com/repos/${REPO}/releases/latest" | grep '"tag_name"' | head -1 | sed 's/.*"tag_name": *"\([^"]*\)".*/\1/')
+
+if [ -z "$TAG" ]; then
+  echo "Error: could not determine latest release"
+  exit 1
+fi
+
+echo "  Latest version: $TAG"
+
+DOWNLOAD_URL="https://github.com/${REPO}/releases/download/${TAG}/${ASSET}"
+
+echo "  Downloading $ASSET..."
+
+# Create temp directory
+TMP_DIR="$(mktemp -d)"
+trap 'rm -rf "$TMP_DIR"' EXIT
+
+curl -fsSL "$DOWNLOAD_URL" -o "${TMP_DIR}/${ASSET}"
+
+# Extract
+echo "  Extracting..."
+if [ "$EXT" = "tar.gz" ]; then
+  tar -xzf "${TMP_DIR}/${ASSET}" -C "$TMP_DIR"
+else
+  unzip -q "${TMP_DIR}/${ASSET}" -d "$TMP_DIR"
+fi
+
+# Find the binary
+BIN_PATH=""
+if [ -f "${TMP_DIR}/${BINARY}" ]; then
+  BIN_PATH="${TMP_DIR}/${BINARY}"
+elif [ -f "${TMP_DIR}/${BINARY}-${OS}-${ARCH}/${BINARY}" ]; then
+  BIN_PATH="${TMP_DIR}/${BINARY}-${OS}-${ARCH}/${BINARY}"
+fi
+
+if [ -z "$BIN_PATH" ]; then
+  echo "Error: could not find ${BINARY} binary in archive"
+  exit 1
+fi
+
+chmod +x "$BIN_PATH"
+
+# Install
+echo "  Installing to ${INSTALL_DIR}/${BINARY}..."
+if [ -w "$INSTALL_DIR" ]; then
+  mv "$BIN_PATH" "${INSTALL_DIR}/${BINARY}"
+else
+  echo "  (requires sudo)"
+  sudo mv "$BIN_PATH" "${INSTALL_DIR}/${BINARY}"
+fi
+
+echo ""
+echo "  Installed transmute $TAG to ${INSTALL_DIR}/${BINARY}"
+echo ""
+echo "  Get started:"
+echo "    transmute *.png          Convert all PNGs"
+echo "    transmute ./files/       Convert all files in a directory"
+echo "    transmute --help         Show all options"
+echo ""