ci(qol): path auto-labeler + stale bot (#949)

* ci(qol): add path auto-labeler, stale bot, PR size labels

* ci(qol): drop PR size labels — not wanted

---------

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

.github/workflows/pr-labeler.yml

@@ -0,0 +1,25 @@
+name: PR Auto-Labeler
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+    branches: [main]
+
+permissions:
+  contents: read
+  pull-requests: write
+
+concurrency:
+  group: labeler-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  label:
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - name: Label by changed files
+        uses: actions/labeler@v6
+        # Reads .github/labeler.yml. Additive only (sync-labels defaults to
+        # false), so manually-added labels and Dependabot's `dependencies`
+        # label are never touched.

.github/workflows/stale.yml

@@ -0,0 +1,38 @@
+name: Stale Bot
+
+on:
+  schedule:
+    # Daily at 06:17 UTC (odd minute to avoid the :00 cron stampede).
+    - cron: "17 6 * * *"
+  workflow_dispatch:
+
+permissions:
+  issues: write
+  pull-requests: write
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - name: Close stale waiting-for-response items
+        uses: actions/stale@v9
+        with:
+          # Only issues/PRs already marked `waiting-for-response` are candidates.
+          # Everything else is left completely alone.
+          only-labels: "waiting-for-response"
+          days-before-stale: 7
+          days-before-close: 7
+          stale-issue-label: "stale"
+          stale-pr-label: "stale"
+          stale-issue-message: >-
+            This has been marked `waiting-for-response` for a week with no reply.
+            It will be closed in another week if there's still no response.
+          stale-pr-message: >-
+            This has been marked `waiting-for-response` for a week with no reply.
+            It will be closed in another week if there's still no response.
+          close-issue-message: >-
+            Closing due to no response. Feel free to reopen anytime!
+          close-pr-message: >-
+            Closing due to no response. Feel free to reopen anytime!
+          operations-per-run: 30