chore: remove duplicate copies of the site, download center and installers (WS-C)

The landing page, download pages, invite page, assetlinks and installers
existed in two or three places; only site/ and the Forgejo feed are served.

- apps/api-server/wwwroot: delete the stale site build, download/invite
  pages, .well-known copy, legacy static admin and 1.0.0 binaries. The API
  no longer serves static files (UseStaticFiles/fallbacks and the apk/zip
  blocker removed); the Next admin is the only admin UI.
- Delete 19 tracked installers/packages (~568 MiB) under site/public/releases,
  apps/web/public/releases and wwwroot/releases; .gitignore blocks them.
- apps/web: delete the download/releases pages, desktop-release.ts, the
  download.html and assetlinks copies, and the accept-invite page (invites
  are only issued to the site's /accept-invite/). e2e specs call the /app
  base path and check the /download redirect instead.
- scripts: delete the retired release/NAS site scripts, drop the web target
  from sync-version, and check assetlinks in site/public only.
- Delete the unused Dockerfile.admin (apps/admin/Dockerfile is used).

Policy: docs/REFACTOR_POLICY.md Wave 3, W3-5 and W3-6.

apps/web/e2e/dashboard-dictionary-commands.spec.ts

@@ -35,7 +35,7 @@ test.describe('Dashboard, dictionary and command Supabase parity', () => {
   let otherId = ''
 
   async function login(page: import('@playwright/test').Page): Promise<void> {
-    await page.goto('/login')
+    await page.goto('/app/login')
     await page.getByPlaceholder('user@studio.com').fill(ownerEmail)
     await page.getByPlaceholder('••••••••').fill(password)
     await page.getByRole('button', { name: '로그인', exact: true }).click()
@@ -146,7 +146,7 @@ test.describe('Dashboard, dictionary and command Supabase parity', () => {
 
   test('dictionary uses RLS CRUD, filters, pagination, duplicate protection and optimistic rollback', async ({ page }) => {
     await login(page)
-    await page.goto('/dictionary')
+    await page.goto('/app/dictionary')
     await expect(page.getByText('CUSTOM DICTIONARY')).toBeVisible()
     await expect(page.getByText(foreignDictionaryWord)).toHaveCount(0)
     await expect(page.getByText(oldestWord)).toHaveCount(0)
@@ -237,7 +237,7 @@ test.describe('Dashboard, dictionary and command Supabase parity', () => {
     expect(bootstrapA.data).toHaveLength(4)
     expect(bootstrapB.data).toHaveLength(4)
     await bootstrapClient.auth.signOut({ scope: 'local' })
-    await page.goto('/commands')
+    await page.goto('/app/commands')
     await expect(page.getByText('SYNCED COMMANDS (4)')).toBeVisible()
     await expect(page.getByText('Translate to English', { exact: true }).first()).toBeVisible()
     await expect(page.getByText('BUILT-IN · READ ONLY').first()).toBeVisible()