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)

package-lock.json

@@ -11,7 +11,8 @@
 				"packages/*"
 			],
 			"dependencies": {
-				"@mariozechner/jailjs": "^0.1.1"
+				"@mariozechner/jailjs": "^0.1.1",
+				"@mariozechner/mini-lit": "^0.1.8"
 			},
 			"devDependencies": {
 				"@biomejs/biome": "^2.1.4",
@@ -816,9 +817,9 @@
 			}
 		},
 		"node_modules/@mariozechner/mini-lit": {
-			"version": "0.1.7",
-			"resolved": "https://registry.npmjs.org/@mariozechner/mini-lit/-/mini-lit-0.1.7.tgz",
-			"integrity": "sha512-P77V7xTaJrc3mocG7wWtxFrhidkBGirD0hRq0aFWpOf+lpjFinkMCnzgY3uB2HcngajDDJpZk5OlvNl+SoiHaw==",
+			"version": "0.1.8",
+			"resolved": "https://registry.npmjs.org/@mariozechner/mini-lit/-/mini-lit-0.1.8.tgz",
+			"integrity": "sha512-7jG0ESWq7emYgyp2xj7osN+DLXGfFkepPZE0nRCoIc7idLXWAGumSz/k7cZxoNyb50iVUGdVzT3rZPr8HtGClw==",
 			"dependencies": {
 				"@preact/signals-core": "^1.12.1",
 				"class-variance-authority": "^0.7.1",
@@ -5516,7 +5517,7 @@
 			"version": "0.5.43",
 			"license": "MIT",
 			"dependencies": {
-				"@mariozechner/mini-lit": "^0.1.7",
+				"@mariozechner/mini-lit": "^0.1.8",
 				"@mariozechner/pi-ai": "^0.5.43",
 				"docx-preview": "^0.3.7",
 				"jszip": "^3.10.1",