build(app): migrate to electron-vite (main/preload/renderer), keep electron-builder (Phase 5d-3a)

Restructure app into src/{main,preload,renderer}; electron.vite.config.ts builds
all three (each main module its own input so CJS requires + the indexer worker
resolve; better-sqlite3 externalized; Vue plugin for renderer). main/index.js
paths updated for the out/ layout + ELECTRON_RENDERER_URL. Still JS/CJS — TS+ESM
and core consumption are the next stages. Verified: npm run dev launches clean;
electron-vite build succeeds; root suite 119/119.

app/electron.vite.config.ts

@@ -0,0 +1,31 @@
+import { resolve } from 'node:path';
+import { defineConfig, externalizeDepsPlugin } from 'electron-vite';
+import vue from '@vitejs/plugin-vue';
+
+// Kept CommonJS for the first electron-vite boot (no "type":"module" yet); the
+// TS + ESM migration is a later stage. Each main-process module is its own input
+// so it is emitted to out/main/<name>.js and the CommonJS require("./x") calls
+// between them (and `new Worker(__dirname/indexer-worker.js)`) resolve at runtime.
+export default defineConfig({
+  main: {
+    plugins: [externalizeDepsPlugin()],
+    build: {
+      rollupOptions: {
+        input: {
+          index: resolve('src/main/index.js'),
+          indexer: resolve('src/main/indexer.js'),
+          'indexer-service': resolve('src/main/indexer-service.js'),
+          'indexer-worker': resolve('src/main/indexer-worker.js'),
+          'indexer-worker-client': resolve('src/main/indexer-worker-client.js'),
+          'recap-capture-query': resolve('src/main/recap-capture-query.js'),
+        },
+      },
+    },
+  },
+  preload: {
+    plugins: [externalizeDepsPlugin()],
+  },
+  renderer: {
+    plugins: [vue()],
+  },
+});