fix(plugin): wire tool.definition handler so todo-description-override actually fires (fixes #3705)

The bundled createTodoDescriptionOverrideHook returns { 'tool.definition': fn }, but plugin-interface.ts never exposes 'tool.definition' as an OpenCode hook handler. Result: the hook is constructed by createToolGuardHooks (line 132-134 of src/plugin/hooks/create-tool-guard-hooks.ts) but the function is never invoked, so todowrite keeps using OpenCode's core 7 KB description instead of the 1.4 KB TODOWRITE_DESCRIPTION. User-defined plugins under ~/.config/opencode/plugin/*.js use the same hook contract and work fine, confirming the contract itself is functional in opencode 1.14.28+.

Fix: add src/plugin/tool-definition.ts (createToolDefinitionHandler) that forwards the OpenCode 'tool.definition' input/output pair into hooks.todoDescriptionOverride. Wire it into plugin-interface.ts alongside tool.execute.before/after.

Regression coverage: src/plugin/tool-definition.test.ts covers (a) todowrite override applied, (b) other tools left untouched, (c) null hook is a no-op.

src/plugin-interface.ts

@@ -8,6 +8,7 @@ import { createCommandExecuteBeforeHandler } from "./plugin/command-execute-befo
 import { createMessagesTransformHandler } from "./plugin/messages-transform"
 import { createSystemTransformHandler } from "./plugin/system-transform"
 import { createEventHandler } from "./plugin/event"
+import { createToolDefinitionHandler } from "./plugin/tool-definition"
 import { createToolExecuteAfterHandler } from "./plugin/tool-execute-after"
 import { createToolExecuteBeforeHandler } from "./plugin/tool-execute-before"
 
@@ -70,6 +71,10 @@ export function createPluginInterface(args: {
       hooks,
     }),
 
+    "tool.definition": createToolDefinitionHandler({
+      hooks,
+    }),
+
     "tool.execute.before": createToolExecuteBeforeHandler({
       ctx,
       hooks,