Merge #181: chore: upgrade Vite v6 → v7 and @sveltejs/vite-plugin-svelte v5 → v6

79024d5 chore: upgrade Vite v6 → v7 and @sveltejs/vite-plugin-svelte v5 → v6 (Jose Celano)

Pull request description:

  ## Overview

  Upgrades Vite and the Svelte Vite plugin together (vite-plugin-svelte v6 requires Vite `^6.3.0 || ^7.0.0`).

  Part of epic #174.

  Closes #170
  Closes #173

  ## Package Changes

  | Package | From | To |
  |---------|------|----|
  | `vite` | `^6.4.1` | `^7.3.1` |
  | `@sveltejs/vite-plugin-svelte` | `^5.1.1` | `^6.2.4` |

  ## Vite v7 Breaking Changes — Assessment

  | Breaking Change | Impact |
  |-----------------|--------|
  | Node.js 18 dropped (requires 20.19+/22.12+) | ✅ None — running Node.js 22 |
  | Default `build.target` → `baseline-widely-available` | ✅ None — aligns with Tailwind v4 which already targets modern browsers |
  | Sass legacy API removed | ✅ None — `vite.config.ts` has no `css.preprocessorOptions` for Sass |
  | `splitVendorChunkPlugin` removed | ✅ None — not used |
  | Advanced API removals (`proxySsrExternalModules`, deprecated types, etc.) | ✅ None — not used |

  No changes to [vite.config.ts](vite.config.ts) were needed.

  ## Testing Checklist

  - [x] `svelte-check`: 0 errors, 0 warnings
  - [x] `npm run build`: success
  - [x] `npm run lint`: success
  - [x] Pre-commit hooks pass
  - [ ] `npm run dev` + HMR works in browser
  - [ ] Production preview works

ACKs for top commit:
  josecelano:
    ACK 79024d5

Tree-SHA512: 64de7cd999b9bd125dd1f3590bad677a1187315f3bd716196f21d84041bebf0a2c61eb9ca93b6c96a627bd4a11fdd3e39b71d924ed294dd3cffd80d821bda88f

Author: josecelano