ci: migrate pytest + Docker to PHCC (retire HA core-checkout harness) (#3)

* openspec: propose migrate-ci-to-phcc (proposal + design)

Design-first per repo convention. Migrates pytest + Docker CI off the dead HA core-checkout harness to the PHCC-based local test suite that already passes locally (164). Implementation (tasks + code) held pending review of the design's open questions.

* ci: migrate pytest + Docker off HA core-checkout to PHCC

Implements openspec change migrate-ci-to-phcc.

- pytest.yaml: run the local PHCC suite (latest + dev matrix; dev is
  continue-on-error). Fixes the trigger (was push:[master] -> never ran on
  main; now main). Drops coverage (was computed but never uploaded). Recipe
  verified in a clean env locally: 164 passed, Python 3.13, latest PHCC.
- Delete dead core-checkout scaffolding: install_dependencies action,
  setup-dependencies, setup-symlinks, update-test-matrix.{py,yaml},
  test_dependencies.py, Dockerfile, docker-build.yml.
- setup-devcontainer: PHCC flow (uv sync --group test).
- tests/README.md: rewritten for 'uv run pytest'.
- CLAUDE.md: drop the 'Refresh test matrix' row.
- hacs.json 2024.12.0 -> 2026.1.0; README min-version line corrected (it
  wrongly claimed '2025.1.0 pinned in manifest.json' - manifest pins none).

* openspec: mark migrate-ci-to-phcc 4.3 done (CI verified green)

.github/workflows/pytest.yaml

@@ -2,77 +2,44 @@ name: pytest
 
 on:
   push:
-    branches: [master]
+    branches: [main]
   pull_request:
 
 jobs:
   pytest:
-    name: Run pytest
+    name: pytest (${{ matrix.name }})
     runs-on: ubuntu-24.04
-    timeout-minutes: 60
+    continue-on-error: ${{ matrix.experimental }}
+    timeout-minutes: 20
     strategy:
       fail-fast: false
       matrix:
         include:
-          - core-version: "2024.12.5"
-            python-version: "3.12"
-          - core-version: "2025.1.4"
-            python-version: "3.12"
-          - core-version: "2025.2.5"
-            python-version: "3.13"
-          - core-version: "2025.3.4"
-            python-version: "3.13"
-          - core-version: "2025.4.4"
-            python-version: "3.13"
-          - core-version: "2025.5.3"
-            python-version: "3.13"
-          - core-version: "2025.6.3"
-            python-version: "3.13"
-          - core-version: "2025.7.4"
-            python-version: "3.13"
-          - core-version: "2025.8.3"
-            python-version: "3.13"
-          - core-version: "2025.9.4"
-            python-version: "3.13"
-          - core-version: "2025.10.4"
-            python-version: "3.13"
-          - core-version: "2025.11.3"
-            python-version: "3.13"
-          - core-version: "2025.12.5"
-            python-version: "3.13"
-          - core-version: "2026.1.3"
-            python-version: "3.13"
-          - core-version: "2026.2.3"
-            python-version: "3.13"
-          - core-version: "2026.3.4"
-            python-version: "3.14.2"
-          - core-version: "2026.4.3"
-            python-version: "3.14.2"
-          - core-version: "dev"
-            python-version: "3.14.2"
+          - name: stable
+            phcc-pre: ""
+            experimental: false
+          - name: dev
+            phcc-pre: "--pre"
+            experimental: true
     steps:
       - name: Check out code from GitHub
         uses: actions/checkout@v6
 
-      - name: Install Home Assistant
-        uses: ./.github/workflows/install_dependencies
-        with:
-          python-version: ${{ matrix.python-version }}
-          core-version: ${{ matrix.core-version }}
+      - name: Set up uv
+        uses: astral-sh/setup-uv@v8.1.0
+
+      - name: Install test dependencies (${{ matrix.name }} PHCC)
+        run: |
+          uv venv --python 3.13
+          uv pip install ${{ matrix.phcc-pre }} \
+            pytest-homeassistant-custom-component \
+            pytest \
+            pytest-asyncio \
+            ulid-transform
 
       - name: Run pytest
-        timeout-minutes: 60
+        env:
+          PYTHONPATH: ${{ github.workspace }}
         run: |
-          export PYTHONPATH=${PYTHONPATH}:${PWD}
           source .venv/bin/activate
-          cd core
-          python3 -X dev -m pytest \
-            -vvv \
-            -qq \
-            --timeout=9 \
-            --durations=10 \
-            --cov=homeassistant.components.adaptive_lighting \
-            --cov-report=xml \
-            -o console_output_style=count \
-            -p no:sugar \
-            tests/components/adaptive_lighting
+          pytest -q