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/App.svelte

@@ -0,0 +1,46 @@
+<script lang="ts">
+  import { onMount } from "svelte";
+  import Router from "svelte-spa-router";
+  import Header from "./components/Header.svelte";
+  import LogViewer from "./routes/LogViewer.svelte";
+  import Models from "./routes/Models.svelte";
+  import Activity from "./routes/Activity.svelte";
+  import { enableAPIEvents } from "./stores/api";
+  import { initScreenWidth, isDarkMode, appTitle, connectionState } from "./stores/theme";
+
+  const routes = {
+    "/": Models,
+    "/logs": LogViewer,
+    "/activity": Activity,
+    "*": Models,
+  };
+
+  // Sync theme to document attribute
+  $effect(() => {
+    document.documentElement.setAttribute("data-theme", $isDarkMode ? "dark" : "light");
+  });
+
+  // Sync title to document
+  $effect(() => {
+    const icon = $connectionState === "connecting" ? "\u{1F7E1}" : $connectionState === "connected" ? "\u{1F7E2}" : "\u{1F534}";
+    document.title = `${icon} ${$appTitle}`;
+  });
+
+  onMount(() => {
+    const cleanupScreenWidth = initScreenWidth();
+    enableAPIEvents(true);
+
+    return () => {
+      cleanupScreenWidth();
+      enableAPIEvents(false);
+    };
+  });
+</script>
+
+<div class="flex flex-col h-screen">
+  <Header />
+
+  <main class="flex-1 overflow-auto p-4">
+    <Router {routes} />
+  </main>
+</div>