fix(dashboard): point updater at new GitHub Pages URL after repo rename

The Tauri auto-updater endpoint was still pointing at
'cortexkit.github.io/opencode-magic-context/latest.json' from before
the repo was renamed to cortexkit/magic-context. After the rename
GitHub Pages does not redirect that subdomain — every Pages URL on
the old name 404s. Anyone running v0.3.4 or v0.4.0 today is silently
frozen at install time because the dashboard polls a dead endpoint
on every startup.

Live verification:
  cortexkit.github.io/opencode-magic-context/latest.json  → 404
  cortexkit.github.io/magic-context/latest.json           → 200

The deploy-updater job in dashboard-release.yml already publishes to
the new URL via GitHub Pages, so once a build with this fix lands in
users' hands, auto-updates work normally for everyone going forward.
v0.3.4 + v0.4.0 users still need a one-time manual download because
the dead URL is baked into their existing binaries.

This fix needs to ship as the next dashboard release before promoting
the download link.

Author: ualtinok

packages/dashboard/src-tauri/tauri.conf.json

@@ -47,7 +47,7 @@
     "updater": {
       "pubkey": "dW50cnVzdGVkIGNvbW1lbnQ6IG1pbmlzaWduIHB1YmxpYyBrZXk6IDY5MUNBMDIxNjUxMEM2MkYKUldRdnhoQmxJYUFjYVU0SlNNbzRWMGJ3MndKOENIVDR0N0N6b0Jyd1l6TUNFTlpZTzV3RXlRYkEK",
       "endpoints": [
-        "https://cortexkit.github.io/opencode-magic-context/latest.json"
+        "https://cortexkit.github.io/magic-context/latest.json"
       ]
     }
   }