Migrate test runner from ts-jest to Vitest

Closes #629.

Switches the test pipeline from `ts-jest`/Jest to Vitest so the test
toolchain aligns with the esbuild-based production build, drops the
`TS5107` workaround we needed in `tsconfig.test.json`, and unblocks the
TypeScript 7 upgrade (which removes `node10` resolution).

- Replace `ts-jest`, `jest`, `jest-environment-jsdom`, `@types/jest`
  with `vitest`, `@vitest/coverage-v8`, `@vitest/ui`, and `jsdom`.
- Add `vitest.config.ts` with jsdom env, path/module aliases that mirror
  the old `moduleNameMapper`, and a small Vite plugin that loads
  `.hbs`/`.md`/`.txt` as raw text (replacement for
  `text-transformer.mjs`).
- Rewrite `test/**` and `__mocks__/**` from `jest.fn`/`jest.mock`/
  `jest.requireActual`/etc. to their `vi` equivalents. Constructor mocks
  use `function`/class syntax so vitest 4.x can call them with `new`.
- Convert mock modules in `__mocks__/` to ESM and import `vi` from
  `vitest`.
- Use `vi.hoisted()` in `mcp-manager.test.ts` for uppercase mock
  identifiers vitest's auto-hoist heuristic doesn't recognize.
- Replace `require('../models')` in `src/services/model-manager.ts`
  with `import * as modelsModule from '../models'` (live binding) so
  the file works under Vite's ESM loader without changing behavior.
- Update tsconfig.test.json: `types: ['vitest/globals', 'node']` and
  drop `ignoreDeprecations: '6.0'`.
- `npm test` now runs `vitest run`; `npm run test:watch` runs the
  watcher. CI's existing `npm test -- --coverage` keeps working
  because vitest accepts `--coverage`.

Docs: AGENTS.md and docs/contributing/tool-development.md now reference
Vitest/`vi.fn()`.

https://claude.ai/code/session_016L3CBfrG11AHHTRegiW89N

Author: claude

AGENTS.md

@@ -207,9 +207,9 @@ if (this.plugin.settings.debugMode) {
 
 ## Testing Guidelines
 
-- Jest with ts-jest for TypeScript support
-- JSDOM environment for DOM testing
-- Test pattern: `**/?(*.)+(spec|test).[tj]s`
+- Vitest (esbuild-powered) for TypeScript support
+- jsdom environment for DOM testing
+- Test pattern: `test/**/?(*.)+(spec|test).[tj]s`
 - Keep unit tests next to implementations and name them after the unit (`models.test.ts`, `main.test.ts`)
 - Assert observable behavior of prompts, services, and tool orchestration; add regression coverage for bugs
 - Extend shared fixtures under `__mocks__/` when mocking new APIs

__mocks__/@google/genai.js

@@ -1,28 +1,27 @@
 // Mock for @google/genai
+import { vi } from 'vitest';
 
-const GoogleGenAI = jest.fn().mockImplementation(() => ({
-	models: {
-		generateContent: jest.fn().mockResolvedValue({
-			response: {
-				text: () => 'Mock response text',
-				candidates: [
-					{
-						groundingMetadata: {
-							webSearchQueries: ['test query'],
-							groundingAttributions: [
-								{
-									uri: 'https://example.com',
-									content: 'Mock content',
-								},
-							],
+export const GoogleGenAI = vi.fn().mockImplementation(function () {
+	return {
+		models: {
+			generateContent: vi.fn().mockResolvedValue({
+				response: {
+					text: () => 'Mock response text',
+					candidates: [
+						{
+							groundingMetadata: {
+								webSearchQueries: ['test query'],
+								groundingAttributions: [
+									{
+										uri: 'https://example.com',
+										content: 'Mock content',
+									},
+								],
+							},
 						},
-					},
-				],
-			},
-		}),
-	},
-}));
-
-module.exports = {
-	GoogleGenAI,
-};
+					],
+				},
+			}),
+		},
+	};
+});

__mocks__/@google/generative-ai.js

@@ -1,28 +1,27 @@
 // Mock for @google/generative-ai
+import { vi } from 'vitest';
 
-const GoogleGenerativeAI = jest.fn().mockImplementation(() => ({
-	getGenerativeModel: jest.fn().mockReturnValue({
-		generateContent: jest.fn().mockResolvedValue({
-			response: {
-				text: () => 'Mock response text',
-				candidates: [
-					{
-						groundingMetadata: {
-							webSearchQueries: ['test query'],
-							groundingAttributions: [
-								{
-									uri: 'https://example.com',
-									content: 'Mock content',
-								},
-							],
+export const GoogleGenerativeAI = vi.fn().mockImplementation(function () {
+	return {
+		getGenerativeModel: vi.fn().mockReturnValue({
+			generateContent: vi.fn().mockResolvedValue({
+				response: {
+					text: () => 'Mock response text',
+					candidates: [
+						{
+							groundingMetadata: {
+								webSearchQueries: ['test query'],
+								groundingAttributions: [
+									{
+										uri: 'https://example.com',
+										content: 'Mock content',
+									},
+								],
+							},
 						},
-					},
-				],
-			},
+					],
+				},
+			}),
 		}),
-	}),
-}));
-
-module.exports = {
-	GoogleGenerativeAI,
-};
+	};
+});