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/ai/src/providers/anthropic.ts

@@ -291,7 +291,16 @@ function buildParams(
 			});
 		}
 	} else if (context.systemPrompt) {
-		params.system = context.systemPrompt;
+		// Add cache control to system prompt for non-OAuth tokens
+		params.system = [
+			{
+				type: "text",
+				text: context.systemPrompt,
+				cache_control: {
+					type: "ephemeral",
+				},
+			},
+		];
 	}
 
 	if (options?.temperature !== undefined) {
@@ -440,6 +449,24 @@ function convertMessages(messages: Message[], model: Model<"anthropic-messages">
 			});
 		}
 	}
+
+	// Add cache_control to the last user message to cache conversation history
+	if (params.length > 0) {
+		const lastMessage = params[params.length - 1];
+		if (lastMessage.role === "user") {
+			// Add cache control to the last content block
+			if (Array.isArray(lastMessage.content)) {
+				const lastBlock = lastMessage.content[lastMessage.content.length - 1];
+				if (
+					lastBlock &&
+					(lastBlock.type === "text" || lastBlock.type === "image" || lastBlock.type === "tool_result")
+				) {
+					(lastBlock as any).cache_control = { type: "ephemeral" };
+				}
+			}
+		}
+	}
+
 	return params;
 }