Fork Notesium source and restructure into Go package layout

Initial fork of github.com/alonswartz/notesium into librenotes:
- Source moved to internal/notesium/ (package notesium)
- Thin entry point at cmd/librenotes/main.go
- Module renamed to git.librete.ch/public/librenotes
- main() exposed as notesium.Run()
- LICENSE preserved (MIT), NOTICE added with attribution
- Web assets and completion.bash co-located with embedding code
  to satisfy go:embed path constraints

Closes #3, #34, #35.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/notesium/web/app/tailwind.config.js

@@ -0,0 +1,9 @@
+/** @type {import('tailwindcss').Config} */
+module.exports = {
+  content: ["*.js", "!vendor.js", "!tailwind.config.js"],
+  darkMode: 'class',
+  theme: {
+    extend: {},
+  },
+  plugins: [],
+}