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/alert.js

@@ -0,0 +1,40 @@
+var t = `
+<div class="pointer-events-auto w-full max-w-sm overflow-hidden rounded-lg bg-white shadow-lg ring-1 ring-black ring-opacity-5">
+  <div class="p-4">
+    <div class="flex items-start">
+      <div class="flex-shrink-0">
+        <div v-if="alert.type == 'error'" class="text-red-400"><Icon name="outline-exclamation-circle" size="h-6 w-6" /></div>
+        <div v-if="alert.type == 'success'" class="text-green-400"><Icon name="outline-check-circle" size="h-6 w-6" /></div>
+      </div>
+      <div class="ml-3 w-0 flex-1 pt-0.5">
+        <p class="text-sm font-medium text-gray-900" v-text="alert.title"></p>
+        <p v-show="alert.body" class="mt-1 text-sm text-gray-500" v-text="alert.body"></p>
+      </div>
+      <div v-show="alert.sticky" class="ml-4 flex flex-shrink-0">
+        <button @click="dismiss()" type="button" class="inline-flex rounded-md bg-white text-gray-400 hover:text-gray-500">
+          <span class="sr-only">Close</span>
+          <Icon name="mini-x-mark" size="h-5 w-5" />
+        </button>
+      </div>
+    </div>
+  </div>
+</div>
+`
+
+import Icon from './icon.js'
+export default {
+  components: { Icon },
+  props: ['alert'],
+  emits: ['alert-dismiss'],
+  methods: {
+    dismiss() {
+      this.$emit('alert-dismiss', this.alert.id);
+    },
+  },
+  mounted() {
+    if (!this.alert.sticky) {
+      setTimeout(() => { this.dismiss(); }, 2000);
+    }
+  },
+  template: t
+}