[P0] Set CODER_URL + CODER_SESSION_TOKEN GH Actions secrets after cluster is up

[ausbru87]

The repo's two GH Actions workflows that touch the live cluster (`push-templates.yml` and `sprint-ticket.yml`) need these two secrets. Without them they fail at the `coder login` step. Currently failing on every push (visible in the Actions tab).

Depends on: the cluster install issue landing first.

Steps

1. Get the Coder URL from TF output:
   ```bash
   cd terraform
   CODER_URL=$(terraform output -raw coder_url)
   echo "$CODER_URL" # https://coder.apps.cluster.rhsummit.coderdemo.io
   ```
2. Open Coder in a browser → log in with kubeadmin password (`terraform output -raw kubeadmin_password_path`, then `cat $(...)`):
   • Set up the first admin user (real email, doesn't matter what for the demo).
   • Create a session token: `Account → Tokens → New token` (or `coder tokens create --lifetime 720h` from CLI).
3. Push to GH:
   ```bash
   gh secret set CODER_URL --body "$CODER_URL"
   gh secret set CODER_SESSION_TOKEN --body ""
   ```

Acceptance criteria

• `gh secret list` shows both `CODER_URL` and `CODER_SESSION_TOKEN`
• Trigger `push-templates.yml` manually (`gh workflow run push-templates.yml`) — completes successfully
• Open a test issue with the `sprint-ticket` label — `sprint-ticket.yml` runs cleanly and comments back with a workspace URL

Don't forget

• The session token has an expiry. Default 30 days. Set `--lifetime 720h` (30d) at minimum, longer if you'd rather not rotate.
• Document who created the token in the team's 1Password / shared notes so we know who to ping when it nears expiry.