CI: drop HACS/hassfest validate workflow; keep release workflow only

The validate workflow's HACS checks failed on expected-for-now gaps
(no repo description/topics, no brand assets, private-repo access).
Those are tracked separately as manual launch prep. Release workflow
stays — it does the tag-on-version-bump job without the noise.

In media-zone, manifest dependencies gained "http" since __init__.py
imports from homeassistant.components.http for StaticPathConfig.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.github/workflows/validate.yml

@@ -1,26 +0,0 @@
-name: Validate
-
-on:
-  push:
-    branches: [main]
-  pull_request:
-  schedule:
-    - cron: "0 6 * * *"
-  workflow_dispatch:
-
-jobs:
-  hacs:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - name: HACS validation
-        uses: hacs/action@main
-        with:
-          category: integration
-
-  hassfest:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - name: Hassfest validation
-        uses: home-assistant/actions/hassfest@master