TEMP: add fail_test dispatch input to validate notify step

One-off scaffolding to push, dispatch with `fail_test=true`, and verify
the new `#crash-bot-ci` Slack notification fires end-to-end. Reverted in
the next commit.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ryan-williams

.github/workflows/daily.yml

@@ -11,6 +11,10 @@ on:
       targets:
         type: string
         description: "Specific DVX targets to run (space-separated .dvc paths, empty = all)"
+      fail_test:
+        type: boolean
+        description: "TEMP: force a deliberate failure (validates notify-on-failure)"
+        default: false
 concurrency:
   group: daily
   cancel-in-progress: false
@@ -151,6 +155,11 @@ jobs:
       - name: Run custom targets
         if: ${{ inputs.targets }}
         run: $DVX ${{ inputs.targets }}
+      - name: TEMP - force test failure
+        if: ${{ inputs.fail_test }}
+        run: |
+          echo "Forcing failure to validate notify-on-failure step."
+          exit 1
       - name: "Notify #crash-bot-ci on failure"
         if: failure()
         env: