Add support for more providers and conversation history (#71)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added multiple new LLM providers (Cerebras, Anthropic, Google AI) and
generic OpenAI-compatible custom providers with runtime registration and
credential handling.
* Conversation persistence with auto-save, save/load/list/delete and
IndexedDB-backed storage.
* New readability-based extractor and semantic content chunking for
large documents.

* **UI/UX Improvements**
* Unified provider settings and "Manage Custom Providers" dialog,
conversation history browser and history dialog integrated into the chat
UI.
* Settings and model selectors generalized to support custom providers.

* **Tests**
* New HTML-to-Markdown evaluation tests and improved large-page
chunking/extraction tooling.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: tysonthomas9

front_end/panels/ai_chat/BUILD.gn

@@ -51,11 +51,10 @@ devtools_module("ai_chat") {
     "ui/settings/components/SettingsFooter.ts",
     "ui/settings/components/AdvancedToggle.ts",
     "ui/settings/providers/BaseProviderSettings.ts",
-    "ui/settings/providers/OpenAISettings.ts",
+    "ui/settings/providers/GenericProviderSettings.ts",
     "ui/settings/providers/LiteLLMSettings.ts",
-    "ui/settings/providers/GroqSettings.ts",
     "ui/settings/providers/OpenRouterSettings.ts",
-    "ui/settings/providers/BrowserOperatorSettings.ts",
+    "ui/settings/providerConfigs.ts",
     "ui/settings/advanced/MCPSettings.ts",
     "ui/settings/advanced/BrowsingHistorySettings.ts",
     "ui/settings/advanced/VectorDBSettings.ts",
@@ -67,8 +66,15 @@ devtools_module("ai_chat") {
     "ui/TodoListDisplay.ts",
     "ui/FileListDisplay.ts",
     "ui/FileContentViewer.ts",
+    "ui/ConversationHistoryList.ts",
+    "ui/conversationHistoryStyles.ts",
+    "ui/CustomProviderDialog.ts",
+    "ui/customProviderStyles.ts",
     "ai_chat_impl.ts",
     "models/ChatTypes.ts",
+    "persistence/ConversationTypes.ts",
+    "persistence/ConversationStorageManager.ts",
+    "persistence/ConversationManager.ts",
     "core/Graph.ts",
     "core/State.ts",
     "core/Types.ts",
@@ -84,6 +90,7 @@ devtools_module("ai_chat") {
     "core/AgentNodes.ts",
     "core/GraphHelpers.ts",
     "core/LLMConfigurationManager.ts",
+    "core/CustomProviderManager.ts",
     "core/ToolNameMap.ts",
     "core/ToolSurfaceProvider.ts",
     "core/StateGraph.ts",
@@ -101,6 +108,10 @@ devtools_module("ai_chat") {
     "LLM/GroqProvider.ts",
     "LLM/OpenRouterProvider.ts",
     "LLM/BrowserOperatorProvider.ts",
+    "LLM/CerebrasProvider.ts",
+    "LLM/AnthropicProvider.ts",
+    "LLM/GoogleAIProvider.ts",
+    "LLM/GenericOpenAIProvider.ts",
     "LLM/MessageSanitizer.ts",
     "LLM/LLMClient.ts",
     "tools/Tools.ts",
@@ -110,6 +121,7 @@ devtools_module("ai_chat") {
     "tools/FinalizeWithCritiqueTool.ts",
     "tools/VisitHistoryManager.ts",
     "tools/HTMLToMarkdownTool.ts",
+    "tools/ReadabilityExtractorTool.ts",
     "tools/SchemaBasedExtractorTool.ts",
     "tools/StreamlinedSchemaExtractorTool.ts",
     "tools/CombinedExtractionTool.ts",
@@ -164,6 +176,7 @@ devtools_module("ai_chat") {
     "evaluation/test-cases/research-agent-tests.ts",
     "evaluation/test-cases/action-agent-tests.ts",
     "evaluation/test-cases/web-task-agent-tests.ts",
+    "evaluation/test-cases/html-to-markdown-tests.ts",
     "evaluation/runner/EvaluationRunner.ts",
     "evaluation/runner/VisionAgentEvaluationRunner.ts",
     "common/MarkdownViewerUtil.ts",
@@ -173,6 +186,8 @@ devtools_module("ai_chat") {
     "common/page.ts",
     "common/WebSocketRPCClient.ts",
     "common/EvaluationConfig.ts",
+    "utils/ContentChunker.ts",
+    "vendor/readability-source.ts",
     "evaluation/remote/EvaluationProtocol.ts",
     "evaluation/remote/EvaluationAgent.ts",
     "tracing/TracingProvider.ts",
@@ -245,11 +260,10 @@ _ai_chat_sources = [
     "ui/settings/components/SettingsFooter.ts",
     "ui/settings/components/AdvancedToggle.ts",
     "ui/settings/providers/BaseProviderSettings.ts",
-    "ui/settings/providers/OpenAISettings.ts",
+    "ui/settings/providers/GenericProviderSettings.ts",
     "ui/settings/providers/LiteLLMSettings.ts",
-    "ui/settings/providers/GroqSettings.ts",
     "ui/settings/providers/OpenRouterSettings.ts",
-    "ui/settings/providers/BrowserOperatorSettings.ts",
+    "ui/settings/providerConfigs.ts",
     "ui/settings/advanced/MCPSettings.ts",
     "ui/settings/advanced/BrowsingHistorySettings.ts",
     "ui/settings/advanced/VectorDBSettings.ts",
@@ -279,6 +293,7 @@ _ai_chat_sources = [
     "core/AgentNodes.ts",
     "core/GraphHelpers.ts",
     "core/LLMConfigurationManager.ts",
+    "core/CustomProviderManager.ts",
     "core/ToolNameMap.ts",
     "core/ToolSurfaceProvider.ts",
     "core/StateGraph.ts",
@@ -296,6 +311,10 @@ _ai_chat_sources = [
     "LLM/GroqProvider.ts",
     "LLM/OpenRouterProvider.ts",
     "LLM/BrowserOperatorProvider.ts",
+    "LLM/CerebrasProvider.ts",
+    "LLM/AnthropicProvider.ts",
+    "LLM/GoogleAIProvider.ts",
+    "LLM/GenericOpenAIProvider.ts",
     "LLM/MessageSanitizer.ts",
     "LLM/LLMClient.ts",
     "tools/Tools.ts",
@@ -305,6 +324,7 @@ _ai_chat_sources = [
     "tools/FinalizeWithCritiqueTool.ts",
     "tools/VisitHistoryManager.ts",
     "tools/HTMLToMarkdownTool.ts",
+    "tools/ReadabilityExtractorTool.ts",
     "tools/SchemaBasedExtractorTool.ts",
     "tools/StreamlinedSchemaExtractorTool.ts",
     "tools/CombinedExtractionTool.ts",
@@ -359,6 +379,7 @@ _ai_chat_sources = [
     "evaluation/test-cases/research-agent-tests.ts",
     "evaluation/test-cases/action-agent-tests.ts",
     "evaluation/test-cases/web-task-agent-tests.ts",
+    "evaluation/test-cases/html-to-markdown-tests.ts",
     "evaluation/runner/EvaluationRunner.ts",
     "evaluation/runner/VisionAgentEvaluationRunner.ts",
     "common/MarkdownViewerUtil.ts",
@@ -368,6 +389,8 @@ _ai_chat_sources = [
     "common/page.ts",
     "common/WebSocketRPCClient.ts",
     "common/EvaluationConfig.ts",
+    "utils/ContentChunker.ts",
+    "vendor/readability-source.ts",
     "evaluation/remote/EvaluationProtocol.ts",
     "evaluation/remote/EvaluationAgent.ts",
     "tracing/TracingProvider.ts",