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/theme.ts

@@ -0,0 +1,53 @@
+import { writable, derived } from "svelte/store";
+import { persistentStore } from "./persistent";
+import type { ScreenWidth } from "../lib/types";
+
+// Persistent stores
+export const isDarkMode = persistentStore<boolean>("theme", false);
+export const appTitle = persistentStore<string>("app-title", "llama-swap");
+
+// Non-persistent stores
+export const screenWidth = writable<ScreenWidth>("md");
+export const connectionState = writable<"connected" | "connecting" | "disconnected">("disconnected");
+
+// Derived store for narrow screens
+export const isNarrow = derived(screenWidth, ($screenWidth) => {
+  return $screenWidth === "xs" || $screenWidth === "sm" || $screenWidth === "md";
+});
+
+// Function to toggle theme
+export function toggleTheme(): void {
+  isDarkMode.update((current) => !current);
+}
+
+// Function to check and update screen width
+export function checkScreenWidth(): void {
+  const innerWidth = window.innerWidth;
+  let newWidth: ScreenWidth;
+
+  if (innerWidth < 640) {
+    newWidth = "xs";
+  } else if (innerWidth < 768) {
+    newWidth = "sm";
+  } else if (innerWidth < 1024) {
+    newWidth = "md";
+  } else if (innerWidth < 1280) {
+    newWidth = "lg";
+  } else if (innerWidth < 1536) {
+    newWidth = "xl";
+  } else {
+    newWidth = "2xl";
+  }
+
+  screenWidth.set(newWidth);
+}
+
+// Initialize screen width and set up resize listener
+export function initScreenWidth(): () => void {
+  checkScreenWidth();
+  window.addEventListener("resize", checkScreenWidth);
+
+  return () => {
+    window.removeEventListener("resize", checkScreenWidth);
+  };
+}