feat(web): componentize frontend and replace native delete confirm

- Split monolithic app.js/style.css into Alpine.js components (icons, store, fileSection, confirm)
- Add central Alpine.store('files') as single source of truth for file lists and actions
- Replace duplicated Inbox/Outbox markup with reusable fileSection component (props: dir, canShare)
- Add shared window.Icons module to remove duplicated inline SVGs
- Replace browser-native confirm() for file deletion with a styled, accessible modal dialog
- Split CSS into design tokens, base, and component layers; modernize visuals
- Update web.go embed and server static routes for the new component/style dirs

web/components/fileSection.js

@@ -0,0 +1,44 @@
+/**
+ * fileSection component.
+ *
+ * A single reusable component parametrized by `dir` and `canShare`. Both the
+ * Inbox and Outbox on the page are the same component instance with different
+ * props, replacing the previously copy-pasted <section> blocks.
+ *
+ * Usage:
+ *   <section x-data="fileSection('inbox', { canShare: true })"> ... </section>
+ */
+(function () {
+  function register() {
+    Alpine.data('fileSection', (dir, opts = {}) => ({
+      dir,
+      canShare: opts.canShare ?? false,
+      dragover: false,
+
+      get files() {
+        return Alpine.store('files').files[dir];
+      },
+      get count() {
+        return this.files.length;
+      },
+      get title() {
+        return dir === 'inbox' ? 'Inbox' : 'Outbox';
+      },
+      get icon() {
+        return dir === 'inbox' ? window.Icons.inbox : window.Icons.outbox;
+      },
+
+      async onSelect(e) {
+        await Alpine.store('files').upload(this.dir, e.target.files);
+        e.target.value = '';
+      },
+
+      async onDrop(e) {
+        await Alpine.store('files').upload(this.dir, e.dataTransfer.files);
+      },
+    }));
+  }
+
+  if (window.Alpine) register();
+  else document.addEventListener('alpine:init', register);
+})();