Add Anthropic prompt caching, pluggable storage, and CORS proxy support

Storage Architecture:
- New pluggable storage system with backends (LocalStorage, ChromeStorage, IndexedDB)
- SettingsRepository for app settings (proxy config, etc.)
- ProviderKeysRepository for API key management
- AppStorage with global accessors (getAppStorage, setAppStorage, initAppStorage)

Transport Refactoring:
- Renamed DirectTransport → ProviderTransport (calls LLM providers with optional CORS proxy)
- Renamed ProxyTransport → AppTransport (uses app server with user auth)
- Updated TransportMode: "direct" → "provider", "proxy" → "app"

CORS Proxy Integration:
- ProviderTransport checks proxy.enabled/proxy.url from storage
- When enabled, modifies model baseUrl to route through proxy: {proxyUrl}/?url={originalBaseUrl}
- ProviderKeyInput test function also honors proxy settings
- Settings dialog with Proxy tab (Switch toggle, URL input, explanatory description)

Anthropic Prompt Caching:
- System prompt cached with cache_control markers (both OAuth and regular API keys)
- Last user message cached to cache conversation history
- Saves 90% on input tokens for cached content (10x cost reduction)

Settings Dialog Improvements:
- Configurable tab system with SettingsTab base class
- ApiKeysTab and ProxyTab as custom elements
- Switch toggle for proxy enable (instead of Checkbox)
- Explanatory paragraphs for each tab
- ApiKeyPromptDialog reuses ProviderKeyInput component

Removed:
- Deprecated ApiKeysDialog (replaced by ProviderKeyInput in SettingsDialog)
- Old storage-adapter and key-store (replaced by new storage architecture)

packages/web-ui/example/src/main.ts

@@ -1,10 +1,13 @@
 import { Button, icon } from "@mariozechner/mini-lit";
 import "@mariozechner/mini-lit/dist/ThemeToggle.js";
-import { ChatPanel, ApiKeysDialog } from "@mariozechner/pi-web-ui";
+import { ApiKeyPromptDialog, ApiKeysTab, ChatPanel, initAppStorage, ProxyTab, SettingsDialog } from "@mariozechner/pi-web-ui";
 import { html, render } from "lit";
 import { Settings } from "lucide";
 import "./app.css";
 
+// Initialize storage with default configuration (localStorage)
+initAppStorage();
+
 const systemPrompt = `You are a helpful AI assistant with access to various tools.
 
 Available tools:
@@ -17,6 +20,9 @@ Feel free to use these tools when needed to provide accurate and helpful respons
 const chatPanel = new ChatPanel();
 chatPanel.systemPrompt = systemPrompt;
 chatPanel.additionalTools = [];
+chatPanel.onApiKeyRequired = async (provider: string) => {
+	return await ApiKeyPromptDialog.prompt(provider);
+};
 
 // Render the app structure
 const appHtml = html`
@@ -32,8 +38,8 @@ const appHtml = html`
 					variant: "ghost",
 					size: "sm",
 					children: icon(Settings, "sm"),
-					onClick: () => ApiKeysDialog.open(),
-					title: "API Keys Settings",
+					onClick: () => SettingsDialog.open([new ApiKeysTab(), new ProxyTab()]),
+					title: "Settings",
 				})}
 			</div>
 		</div>