fix(console): pass download channels through and alias stable to latest - #60778

Issue for this PR

Closes #

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

/download/[channel]/[platform] only knew stable vs everything else, so /download/dev/<platform> (and any unknown channel) silently redirected to the beta build.

• The route now passes the channel straight to the update API (/update/api/<channel>/desktop/opencode). The only mapping is stable → latest, kept as a permanent alias with a comment: stable is what the download page linked to for months and ~10% of its traffic (~45k requests/week) comes from outside opencode.ai (bookmarks, other sites, curl/wget scripts).
• The two identical per-channel asset maps become one. Unknown platform → 404; unknown channel → whatever status the update API returns.
• The download page now links to /download/latest/<platform>.

How did you verify your code works?

bun typecheck and bun run typecheck:tsc in packages/console/app, bun run check at the root. Checked that the update API serves latest, beta and dev. Will check the deployed redirects with curl after merge.

Visual

<svg xmlns="http://www.w3.org/2000/svg" width="240" height="72" viewBox="0 0 240 72" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" font-family="ui-monospace,monospace" font-size="12">
  <style>@keyframes d{0%,20%{transform:translateY(-6px);opacity:.3}50%,100%{transform:none;opacity:1}}.a{animation:d 2s ease-in-out infinite alternate}@media (prefers-reduced-motion:reduce){.a{animation:none}}</style>
  <text x="16" y="40" fill="currentColor" stroke="none" opacity=".5">stable</text>
  <path d="M70 36h40m-6-6 6 6-6 6" opacity=".5"/>
  <g class="a"><path d="M140 22v20m-7-7 7 7 7-7M131 50h18"/></g>
  <text x="160" y="40" fill="currentColor" stroke="none">latest</text>
</svg>

Screenshots / recordings

Not a UI change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR