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

hatch_build.py

@@ -0,0 +1,68 @@
+"""Custom hatchling build hook: build the React frontend if it is missing or stale.
+
+This makes NVCurve installable with a single command, e.g.::
+
+    uv tool install "git+https://gitea.zephyre.one/Pakobbix/nvcurve.git"
+
+The hook runs inside the isolated build environment right before the wheel
+(or sdist) is assembled. If ``frontend/dist`` does not exist yet — or is older
+than the frontend sources — it compiles the frontend using the host's ``npm``
+(PATH is inherited from the environment).
+"""
+
+from __future__ import annotations
+
+import os
+import shutil
+import subprocess
+import sys
+
+from hatchling.builders.hooks.plugin.interface import BuildHookInterface
+
+# Frontend inputs that must be newer than dist/index.html to trigger a rebuild.
+_FRONTEND_INPUTS = ("src", "index.html", "vite.config.ts", "package.json", "tsconfig.json")
+
+
+class FrontendBuildHook(BuildHookInterface):
+    """Build ``frontend/dist`` with npm when it is missing or stale."""
+
+    PLUGIN_NAME = "custom"
+
+    def initialize(self, version: str, build_data: dict) -> None:
+        frontend = os.path.join(self.root, "frontend")
+        dist_index = os.path.join(frontend, "dist", "index.html")
+
+        if not self._needs_build(frontend, dist_index):
+            return
+
+        npm = shutil.which("npm")
+        if npm is None:
+            raise RuntimeError(
+                "npm not found on PATH. Node.js 18+ and npm are required to build "
+                "the NVCurve frontend. Install them and retry, or use install.sh "
+                "which checks prerequisites for you."
+            )
+
+        print(
+            "[nvcurve] frontend/dist missing or stale — building frontend with npm ...",
+            file=sys.stderr,
+        )
+        subprocess.run([npm, "ci", "--no-audit", "--no-fund"], cwd=frontend, check=True)
+        subprocess.run([npm, "run", "build"], cwd=frontend, check=True)
+
+    @staticmethod
+    def _needs_build(frontend: str, dist_index: str) -> bool:
+        if not os.path.isfile(dist_index):
+            return True
+        dist_mtime = os.path.getmtime(dist_index)
+        for name in _FRONTEND_INPUTS:
+            path = os.path.join(frontend, name)
+            if os.path.isfile(path):
+                if os.path.getmtime(path) > dist_mtime:
+                    return True
+            elif os.path.isdir(path):
+                for root, _dirs, files in os.walk(path):
+                    for file in files:
+                        if os.path.getmtime(os.path.join(root, file)) > dist_mtime:
+                            return True
+        return False