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/stores/persistent.ts

@@ -0,0 +1,31 @@
+import { writable, type Writable } from "svelte/store";
+
+export function persistentStore<T>(key: string, initialValue: T): Writable<T> {
+  // Get initial value from localStorage or use default
+  let storedValue = initialValue;
+  if (typeof window !== "undefined") {
+    try {
+      const saved = localStorage.getItem(key);
+      if (saved !== null) {
+        storedValue = JSON.parse(saved);
+      }
+    } catch (e) {
+      console.error(`Error parsing stored value for ${key}`, e);
+    }
+  }
+
+  const store = writable<T>(storedValue);
+
+  // Subscribe to changes and save to localStorage
+  store.subscribe((value) => {
+    if (typeof window !== "undefined") {
+      try {
+        localStorage.setItem(key, JSON.stringify(value));
+      } catch (e) {
+        console.error(`Error saving value for ${key}`, e);
+      }
+    }
+  });
+
+  return store;
+}