chore: upgrade to vite 6 (#14363)

Upgrades the frontend toolchain to Vite 6 and tidies up the build config
along the way. Behavior is unchanged for end users; this is dev/build
infra.

## What changed
- `vite` 5.4 → 6.4, `@vitejs/plugin-vue` → 5.2, `vite-plugin-ruby` → 5.2
(with matching `vite_rails`/`vite_ruby` gem bumps).
- Dropped the `vite-node` 2.0.1 pnpm override — no longer needed now
that vitest 3 runs on Vite 6 directly.
- Split the single `vite.config.ts` into:
- `vite.config.ts` (app), `vite.lib.config.ts` (SDK), `vite.shared.ts`
(aliases / Vue options), `vitest.config.ts` (tests).
- `pnpm build:sdk` now selects the SDK config explicitly instead of
branching on `BUILD_MODE=library`. SDK output path is unchanged
(`public/packs/js/sdk.js`).

No changes needed to Docker images, deployment scripts, or CI — Node 24
and pnpm 10 are already past Vite 6's floor, and the rake
`assets:precompile` hook still drives the SDK build via `pnpm`.

## How to test
- `pnpm dev` and verify the dashboard, widget, and survey routes load
and HMR works.
- Load a Chatwoot site widget on a test page and confirm `sdk.js` is
served and the widget mounts.
- `RAILS_ENV=production bundle exec rake assets:precompile` and confirm
`public/packs/js/sdk.js` plus the rest of the manifest are produced.
- `pnpm test` for the JS suite.

---------

Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>
Co-authored-by: Sony Mathew <2040199+sony-mathew@users.noreply.github.com>

package.json

@@ -12,7 +12,7 @@
     "start:test": "RAILS_ENV=test foreman start -f ./Procfile.test",
     "dev": "overmind start -f ./Procfile.dev",
     "ruby:prettier": "bundle exec rubocop -a",
-    "build:sdk": "BUILD_MODE=library vite build",
+    "build:sdk": "vite build --config vite.lib.config.ts",
     "prepare": "husky install",
     "size": "size-limit",
     "story:dev": "histoire dev",
@@ -53,7 +53,7 @@
     "@tailwindcss/typography": "^0.5.19",
     "@tanstack/vue-table": "^8.20.5",
     "@twilio/voice-sdk": "^2.12.4",
-    "@vitejs/plugin-vue": "^5.1.4",
+    "@vitejs/plugin-vue": "^5.2.4",
     "@vue/compiler-sfc": "^3.5.8",
     "@vuelidate/core": "^2.0.3",
     "@vuelidate/validators": "^2.0.4",
@@ -146,8 +146,8 @@
     "prosemirror-model": "^1.22.3",
     "size-limit": "^8.2.4",
     "tailwindcss": "^3.4.19",
-    "vite": "^5.4.21",
-    "vite-plugin-ruby": "^5.0.0",
+    "vite": "6.4.2",
+    "vite-plugin-ruby": "^5.2.1",
     "vitest": "3.0.5"
   },
   "engines": {
@@ -161,8 +161,7 @@
   },
   "pnpm": {
     "overrides": {
-      "vite-node": "2.0.1",
-      "vite": "5.4.21",
+      "vite": "6.4.2",
       "vitest": "3.0.5",
       "minimatch@<4": "3.1.5",
       "minimatch@>=9.0.0 <9.0.7": "9.0.9",