fix: replace emoji icons with inline SVG (Icon.svelte + icons.js)

All emoji characters replaced with inline SVG icons:
- Plugin Manager sidebar: puzzle SVG icon
- Verstak logo: stack/tray SVG icon
- Plugin icons: flask SVG (from plugin manifest)
- Warning/error indicators: warning triangle SVG
- Settings button: gear SVG
- Vault recent: vault/shield SVG
- Fallback: dot SVG

New components:
- frontend/src/lib/ui/icons.js — SVG path map
- frontend/src/lib/ui/Icon.svelte — reusable SVG icon component

Icon policy: NO emoji or unicode pictographic symbols in the app.
Only SVG icons registered in icons.js are allowed.
Wails WebKitGTK does not render colour emoji.

frontend/src/lib/ui/Icon.svelte

@@ -0,0 +1,33 @@
+<script>
+  /**
+   * Icon.svelte — Renders inline SVG icons.
+   *
+   * Usage:
+   *   <Icon name="puzzle" size={18} />
+   *   <Icon name="flask" class="my-icon" />
+   *
+   * Rules:
+   *   - NO emoji, NO unicode pictographic symbols
+   *   - ALL icons must be SVG registered in ../ui/icons.js
+   *   - If name is not found, renders a default dot icon
+   */
+  import { iconPaths } from './icons.js';
+
+  export let name = 'dot';
+  export let size = 16;
+  export let className = '';
+
+  $: icon = iconPaths[name] || iconPaths.dot;
+</script>
+
+<svg
+  xmlns="http://www.w3.org/2000/svg"
+  viewBox={icon.viewBox}
+  width={size}
+  height={size}
+  class={className}
+>
+  {#each icon.paths as p}
+    <path d={p.d} {...p.attrs} />
+  {/each}
+</svg>