ui-svelte: add Svelte port of React UI (#487)

Trying out svelte for the UI. The port was done by Claude Code on the iOS app w/ Opus 4.5. 

---

* ui: add Svelte port of React UI

Port the React-based UI to Svelte 5 with the following changes:

- Create new ui-svelte directory with complete Svelte 5 implementation
- Use Svelte stores instead of React contexts for state management
- Implement custom ResizablePanels component to replace react-resizable-panels
- Port all pages: LogViewer, Models, Activity
- Port all components: Header, ConnectionStatus, LogPanel, ModelsPanel, etc.
- Use svelte-spa-router for client-side routing
- Same build output directory (proxy/ui_dist) and base path (/ui/)
- Tailwind CSS 4 with same theme configuration

https://claude.ai/code/session_01F3xXLYsd62gePVSFv7aboP

* ui-svelte: simplify state management

- Remove redundant state syncing pattern in LogPanel and ModelsPanel
- Use store values directly with $ syntax instead of manual subscriptions
- Consolidate duplicate title sync logic in App.svelte
- Use existing syncTitleToDocument() from theme.ts

https://claude.ai/code/session_01F3xXLYsd62gePVSFv7aboP

* ui-svelte: use idiomatic Svelte 5 patterns

- Use $effect for document side effects (theme, title) instead of
  store subscriptions
- Use class: directive for active nav links in Header
- Remove SSR guards (unnecessary for client-only SPA)
- Remove leaked subscription in syncThemeToDocument
- Simplify theme.ts by removing sync functions

https://claude.ai/code/session_01F3xXLYsd62gePVSFv7aboP

* ui-svelte: fix build warnings and improve accessibility

Fix Svelte build warnings and add proper accessibility support
to interactive components.

- add aria-labels to buttons for screen readers
- implement keyboard navigation for resizable separator
- suppress intentional state initialization warnings
- update Makefile to use ui-svelte build directory
- add peer:true to package-lock.json dependencies

* ui-svelte: reorganize navigation and add log view toggle

Make Models the default landing page and add view mode toggle
to the Logs page with persistent state.

- set Models as default route at /
- move Logs to /logs route
- reorder navigation: Models, Activity, Logs
- add view toggle with three modes: Panels, Proxy only, Upstream only
- fix horizontal overflow with width constraints

ui-svelte/src/routes/LogViewer.svelte

@@ -0,0 +1,75 @@
+<script lang="ts">
+  import { proxyLogs, upstreamLogs } from "../stores/api";
+  import { screenWidth } from "../stores/theme";
+  import { persistentStore } from "../stores/persistent";
+  import LogPanel from "../components/LogPanel.svelte";
+  import ResizablePanels from "../components/ResizablePanels.svelte";
+
+  type ViewMode = "proxy" | "upstream" | "panels";
+
+  const viewModeStore = persistentStore<ViewMode>("logviewer-view-mode", "panels");
+
+  let direction = $derived<"horizontal" | "vertical">(
+    $screenWidth === "xs" || $screenWidth === "sm" ? "vertical" : "horizontal"
+  );
+
+  function cycleViewMode(): void {
+    const modes: ViewMode[] = ["panels", "proxy", "upstream"];
+    const currentIndex = modes.indexOf($viewModeStore);
+    const nextIndex = (currentIndex + 1) % modes.length;
+    viewModeStore.set(modes[nextIndex]);
+  }
+
+  function getViewModeIcon(mode: ViewMode): string {
+    switch (mode) {
+      case "proxy":
+        return "P";
+      case "upstream":
+        return "U";
+      case "panels":
+        return "⊞";
+    }
+  }
+
+  function getViewModeLabel(mode: ViewMode): string {
+    switch (mode) {
+      case "proxy":
+        return "Proxy";
+      case "upstream":
+        return "Upstream";
+      case "panels":
+        return "Panels";
+    }
+  }
+</script>
+
+<div class="flex flex-col h-full w-full gap-2">
+  <div class="flex items-center gap-2">
+    <button
+      onclick={cycleViewMode}
+      class="btn flex items-center gap-2 text-sm"
+      title="Toggle view mode"
+      aria-label="Toggle view mode: {getViewModeLabel($viewModeStore)}"
+    >
+      <span class="font-mono font-bold">{getViewModeIcon($viewModeStore)}</span>
+      <span>{getViewModeLabel($viewModeStore)}</span>
+    </button>
+  </div>
+
+  <div class="flex-1 w-full overflow-hidden">
+    {#if $viewModeStore === "panels"}
+      <ResizablePanels {direction} storageKey="logviewer-panel-group">
+        {#snippet leftPanel()}
+          <LogPanel id="proxy" title="Proxy Logs" logData={$proxyLogs} />
+        {/snippet}
+        {#snippet rightPanel()}
+          <LogPanel id="upstream" title="Upstream Logs" logData={$upstreamLogs} />
+        {/snippet}
+      </ResizablePanels>
+    {:else if $viewModeStore === "proxy"}
+      <LogPanel id="proxy" title="Proxy Logs" logData={$proxyLogs} />
+    {:else}
+      <LogPanel id="upstream" title="Upstream Logs" logData={$upstreamLogs} />
+    {/if}
+  </div>
+</div>