chore(wailsv3): v3 conformance pass over project files

Fixes the wails3 dev boot failure and removes remaining v2-isms so the tree matches a stock v3 project.

- frontend/package.json: add missing build:dev script (vite build --minify false --mode development). The dev taskflow runs npm run build:dev, which v2-era package.json never had - this was the wails3 dev boot failure.
- frontend/vite.config.ts: add the @wailsio/runtime vite plugin (typed custom events, as in every v3 template) and the server host/port/strictPort block (5173, matching the dev task).
- Remove stale v2 build dirs build/darwin + build/windows (v2 wails scaffolding; v3 generates its own via build-assets if ever needed).
- Delete untracked frontend/package.json.md5 (v2 change-detection artifact; v3 Taskfile uses content-hash sources) and drop its gitignore rule.
- go.mod: delete the leftover commented-out v2 replace directive.
- README.md: dev/build docs updated to make dev / make build (wails3), dropping the v2 :34115 browser-server paragraph; install link points at v3 docs.

Verified: production vite build green with the plugin, and wails3 dev boots end-to-end (bindings regen, build:dev, vite on :5173, asset server connected, AniTrack 1.6.8 window mapped).

frontend/package.json

@@ -5,6 +5,7 @@
   "type": "module",
   "scripts": {
     "dev": "vite",
+    "build:dev": "vite build --minify false --mode development",
     "build": "vite build",
     "preview": "vite preview",
     "check": "svelte-check --tsconfig ./tsconfig.json"

frontend/vite.config.ts

@@ -1,7 +1,13 @@
 import {defineConfig} from 'vite'
 import {svelte} from '@sveltejs/vite-plugin-svelte'
+import wails from '@wailsio/runtime/plugins/vite'
 
 // https://vitejs.dev/config/
 export default defineConfig({
-  plugins: [svelte()]
+  server: {
+    host: '127.0.0.1',
+    port: Number(process.env.WAILS_VITE_PORT) || 5173,
+    strictPort: true,
+  },
+  plugins: [svelte(), wails('./bindings')]
 })