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/pane.js

@@ -0,0 +1,71 @@
+var t = `
+<div class="relative flex-none" :style="{ width: paneWidth + 'px' }">
+  <div class="flex flex-col h-full w-full">
+    <slot></slot>
+  </div>
+  <div v-show="resizing" v-text="paneWidth + 'px'" class="absolute bottom-0 right-0 p-4 text-gray-400 text-xs"></div>
+  <div @dblclick="setDefaultWidth()" @mousedown="startResize"
+    :class="direction == 'right' ? 'left-full pl-1.5 mr-1.5' : 'right-full pr-1.5 ml-1.5'"
+    class="z-50 absolute group inset-y-0 cursor-ew-resize flex items-center">
+    <div class="h-8 w-1 rounded-full group-hover:bg-gray-300"></div>
+  </div>
+</div>
+`
+
+export default {
+  props: {
+    name: { type: String },
+    defaultWidth: { type: Number, default: 200 },
+    minWidth: { type: Number, default: 100 },
+    direction: { type: String, default: "right" },
+  },
+  data() {
+    return {
+      paneWidth: null,
+      maxWidth: null,
+      startResizeClientX: null,
+      startResizePaneWidth: null,
+      resizing: false,
+    }
+  },
+  methods: {
+    startResize(event) {
+      this.startResizeClientX = event.clientX;
+      this.startResizePaneWidth = this.paneWidth;
+      this.maxWidth = this.$el.parentElement.offsetWidth - 50;
+      this.resizing = true;
+      event.preventDefault();
+      document.addEventListener('mousemove', this.doResize);
+      document.addEventListener('mouseup', this.stopResize);
+    },
+    doResize(event) {
+      let draggedDistance = event.clientX - this.startResizeClientX;
+      if (this.direction === 'left') draggedDistance = -draggedDistance;
+      const newWidth = this.startResizePaneWidth + draggedDistance;
+      if (newWidth <= this.maxWidth && newWidth >= this.minWidth ) this.paneWidth = newWidth;
+    },
+    stopResize() {
+      this.resizing = false;
+      this.savePreferredWidth();
+      document.removeEventListener('mousemove', this.doResize);
+      document.removeEventListener('mouseup', this.stopResize);
+    },
+    setDefaultWidth() {
+      this.paneWidth = this.defaultWidth;
+      this.savePreferredWidth()
+    },
+    savePreferredWidth() {
+      const key = `${this.name}Width`;
+      this.$notesiumState[key] = this.paneWidth;
+    },
+    loadPreferredWidth() {
+      const key = `${this.name}Width`;
+      this.paneWidth = parseInt(this.$notesiumState[key], 10) || this.defaultWidth;
+    },
+  },
+  mounted() {
+    this.loadPreferredWidth();
+  },
+  template: t
+}
+