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.

site/public/releases/1.0.0/latest.yml

@@ -1,8 +0,0 @@
-version: 1.0.0
-files:
-  - url: D3RO-Voice-Setup-1.0.0-x64.exe
-    sha512: Ae4ZDaqL6mtkpyGsX9rna6WT3hhtChiEF4hl+Yx1CQvjCPwTq7LmhcBEm40TvRHOVtjQSASsCTs1wxVgSRo1Ow==
-    size: 102123822
-path: D3RO-Voice-Setup-1.0.0-x64.exe
-sha512: Ae4ZDaqL6mtkpyGsX9rna6WT3hhtChiEF4hl+Yx1CQvjCPwTq7LmhcBEm40TvRHOVtjQSASsCTs1wxVgSRo1Ow==
-releaseDate: '2026-08-20T01:56:59.299Z'

site/public/releases/latest.yml

@@ -1,8 +0,0 @@
-version: 1.0.0
-files:
-  - url: D3RO-Voice-Setup-1.0.0-x64.exe
-    sha512: Ae4ZDaqL6mtkpyGsX9rna6WT3hhtChiEF4hl+Yx1CQvjCPwTq7LmhcBEm40TvRHOVtjQSASsCTs1wxVgSRo1Ow==
-    size: 102123822
-path: D3RO-Voice-Setup-1.0.0-x64.exe
-sha512: Ae4ZDaqL6mtkpyGsX9rna6WT3hhtChiEF4hl+Yx1CQvjCPwTq7LmhcBEm40TvRHOVtjQSASsCTs1wxVgSRo1Ow==
-releaseDate: '2026-08-20T01:56:59.299Z'