feat: add native runtime customization

OpenCode and Continue customization was previously planned but unavailable, and Runtime-native capabilities were not represented consistently across providers. GoodBuddy now provides secure Main-owned customization settings, truthful native inventories, OpenCode Agents and Commands, Continue Rules and Prompts, DSH Web Search/Fetch, MCP Prompt and Resource metadata, and manual compaction where supported.

Native capabilities are presented in eleven accessible tabs with Tools separated from Commands, LSP, and Formatters. Tool source and Ask/Execute availability are explicit, external OpenCode remains connection-only, Continue reports unsupported static tool discovery instead of advertising unreachable Skills, and disposable inventory probes avoid retaining background runtimes.

Ask remains read-only at the Runtime boundary, Execute keeps the existing authorization controls, and credentials remain confined to Main.

Release note: 新增 OpenCode、Continue 与 DeepSeek Harness 的 Runtime 原生定制与真实能力清单；工具来源、Ask/Execute 可用性、上下文压缩和 MCP 元数据现在可清晰查看，同时继续保持 Main 进程凭据保护与现有权限边界。

src/shared/assistant-contracts.ts

@@ -234,6 +234,19 @@ export type ConversationMessage = z.infer<
   typeof conversationMessageSchema
 >
 
+export const maximumConversationHistoryMessages = 500
+export const maximumConversationHistoryCharacters = 2_000_000
+export const conversationHistoryMessageSchema =
+  conversationMessageSchema
+    .pick({
+      role: true,
+      content: true
+    })
+    .extend({
+      content: z.string().max(100_000)
+    })
+    .strict()
+
 export const conversationContextMetricsSchema = z
   .object({
     runtimeSelectionKey: z.string().trim().min(1).max(1_000),