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/src/state/agent-session.ts

@@ -10,8 +10,8 @@ import {
 } from "@mariozechner/pi-ai";
 import type { AppMessage } from "../components/Messages.js";
 import type { Attachment } from "../utils/attachment-utils.js";
-import { DirectTransport } from "./transports/DirectTransport.js";
-import { ProxyTransport } from "./transports/ProxyTransport.js";
+import { AppTransport } from "./transports/AppTransport.js";
+import { ProviderTransport } from "./transports/ProviderTransport.js";
 import type { AgentRunConfig, AgentTransport } from "./transports/types.js";
 import type { DebugLogEntry } from "./types.js";
 
@@ -35,7 +35,7 @@ export type AgentSessionEvent =
 	| { type: "error-no-model" }
 	| { type: "error-no-api-key"; provider: string };
 
-export type TransportMode = "direct" | "proxy";
+export type TransportMode = "provider" | "app";
 
 export interface AgentSessionOptions {
 	initialState?: Partial<AgentSessionState>;
@@ -69,12 +69,12 @@ export class AgentSession {
 		this.messagePreprocessor = opts.messagePreprocessor;
 		this.debugListener = opts.debugListener;
 
-		const mode = opts.transportMode || "direct";
+		const mode = opts.transportMode || "provider";
 
-		if (mode === "proxy") {
-			this.transport = new ProxyTransport(async () => this.preprocessMessages());
+		if (mode === "app") {
+			this.transport = new AppTransport(async () => this.preprocessMessages());
 		} else {
-			this.transport = new DirectTransport(async () => this.preprocessMessages());
+			this.transport = new ProviderTransport(async () => this.preprocessMessages());
 		}
 	}