Add single-command installation: install.sh, Makefile, frontend build hook

- hatch_build.py: custom hatchling build hook that compiles the React
  frontend (npm ci + build) when frontend/dist is missing or stale, so
  'uv tool install git+https://gitea.zephyre.one/Pakobbix/nvcurve.git'
  works as a single command
- install.sh: curl|bash installer (checks prerequisites, auto-installs uv,
  clones and installs)
- Makefile: dev targets (frontend, install, dev, test, clean)
- README/docs: document the one-liner, clone, and direct-git installs

install.sh

@@ -0,0 +1,62 @@
+#!/usr/bin/env bash
+#
+# NVCurve single-command installer.
+#
+#   curl -fsSL https://gitea.zephyre.one/Pakobbix/nvcurve/raw/branch/main/install.sh | bash
+#
+# or from a local clone:
+#
+#   git clone https://gitea.zephyre.one/Pakobbix/nvcurve.git && cd nvcurve && ./install.sh
+#
+# The React frontend is compiled automatically during the Python build
+# (see hatch_build.py), so Node.js 18+ and npm must be available.
+#
+# Environment:
+#   NVCURVE_BRANCH  branch to install (default: main)
+
+set -euo pipefail
+
+REPO_URL="https://gitea.zephyre.one/Pakobbix/nvcurve.git"
+BRANCH="${NVCURVE_BRANCH:-main}"
+
+fail() {
+    echo "error: $*" >&2
+    exit 1
+}
+
+# --- prerequisites -----------------------------------------------------------
+command -v git >/dev/null 2>&1 \
+    || fail "git is required. Install it first."
+command -v node >/dev/null 2>&1 \
+    || fail "Node.js 18+ is required (e.g. 'sudo pacman -S nodejs npm' or 'sudo apt install nodejs npm')."
+command -v npm >/dev/null 2>&1 \
+    || fail "npm is required (usually installed together with Node.js)."
+
+if ! command -v uv >/dev/null 2>&1; then
+    echo "uv not found — installing it from https://astral.sh/uv ..."
+    curl -LsSf https://astral.sh/uv/install.sh | sh
+    export PATH="$HOME/.local/bin:$PATH"
+    command -v uv >/dev/null 2>&1 \
+        || fail "uv installation failed. Install uv manually: https://docs.astral.sh/uv/"
+fi
+
+# --- locate the source tree ---------------------------------------------------
+if [ -f pyproject.toml ] && [ -d frontend ]; then
+    src="$(pwd)"
+    echo "Installing from current directory: $src"
+else
+    tmp="$(mktemp -d)"
+    trap 'rm -rf "$tmp"' EXIT
+    echo "Cloning $REPO_URL (branch: $BRANCH) ..."
+    git clone --quiet --depth 1 --branch "$BRANCH" "$REPO_URL" "$tmp/nvcurve"
+    src="$tmp/nvcurve"
+fi
+
+# --- install -------------------------------------------------------------------
+# The frontend is built automatically by the build hook (hatch_build.py).
+uv tool install --force "$src"
+
+echo
+echo "NVCurve installed."
+echo "  Verify your GPU:  nvcurve setup"
+echo "  Start the web UI: nvcurve"