ui: convert ActivityTable to shadcn-svelte data-table

Replace the hand-rolled table with a TanStack Table-backed shadcn
data-table using the FlexRender/createSvelteTable helpers, with
DropdownMenu column visibility, Select page-size, and icon-button
pagination. Column visibility and page size persist to localStorage.

Move tooltip usage to the canonical shadcn-svelte pattern by adding a
single root Tooltip.Provider in App.svelte and using Tooltip.Root/
Trigger/Content directly in the activity-table sub-components
(HeaderLabel, MetaCell), dropping the custom Tooltip/MetadataTooltip
wrappers.

- add @tanstack/table-core and shadcn data-table helpers
- split cell/header renderers into activity-table/* sub-components
- switch pagination/visibility to TanStack Table state driven by
  table.nextPage/previousPage/setPageIndex/setPageSize and
  column.toggleVisibility

ui-svelte/package-lock.json

@@ -8,6 +8,7 @@
       "name": "ui-svelte",
       "version": "0.0.0",
       "dependencies": {
+        "@tanstack/table-core": "^8.21.3",
         "chart.js": "4.5.1",
         "highlight.js": "^11.11.1",
         "katex": "^0.16.28",
@@ -817,6 +818,19 @@
         "vite": "^5.2.0 || ^6 || ^7"
       }
     },
+    "node_modules/@tanstack/table-core": {
+      "version": "8.21.3",
+      "resolved": "https://registry.npmjs.org/@tanstack/table-core/-/table-core-8.21.3.tgz",
+      "integrity": "sha512-ldZXEhOBb8Is7xLs01fR3YEc3DERiz5silj8tnGkFZytt1abEvl/GhUmCE0PMLaMPTa3Jk4HbKmRlHmu+gCftg==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=12"
+      },
+      "funding": {
+        "type": "github",
+        "url": "https://github.com/sponsors/tannerlinsley"
+      }
+    },
     "node_modules/@tsconfig/svelte": {
       "version": "5.0.8",
       "resolved": "https://registry.npmjs.org/@tsconfig/svelte/-/svelte-5.0.8.tgz",