CI: Node 24 actions, pip on PEP 668 runner images, drop committed build cache

- actions/checkout@v7 and tj-actions/changed-files@v47 (Node 20 is deprecated)
- PIP_BREAK_SYSTEM_PACKAGES for Gitea's runner image (externally-managed Python)
- untrack common/.esphome (a gitlink with no submodule mapping) and ignore
  .esphome/ in every directory

.github/workflows/ci.yml

@@ -10,11 +10,11 @@ jobs:
     name: YAML lint
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v7
 
       - name: Get changed YAML files
         id: changed
-        uses: tj-actions/changed-files@v46
+        uses: tj-actions/changed-files@v47
         with:
           files: "**/*.yaml"
 
@@ -28,16 +28,19 @@ jobs:
     name: ESPHome config validation
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v7
 
       - name: Get changed device configs
         id: changed
-        uses: tj-actions/changed-files@v46
+        uses: tj-actions/changed-files@v47
         with:
           files: "mcu-*.yaml"
 
       - name: Install ESPHome (dev)
         if: steps.changed.outputs.any_changed == 'true'
+        # Gitea's runner image marks the system Python as externally managed (PEP 668)
+        env:
+          PIP_BREAK_SYSTEM_PACKAGES: "1"
         run: pip install git+https://github.com/esphome/esphome.git@dev
 
       - name: Prepare secrets

.gitignore

@@ -2,7 +2,7 @@
 # This is an example and may include too much for your use-case.
 # You can modify this file to suit your needs.
 /.claude/
-/.esphome/
+.esphome/
 /secrets.yaml
 /archive/
 /trash/