ci: add standard centralized workflows (#609)

Add missing standard SciML centralized caller workflows:
- RunicSuggestions.yml (Runic auto-format suggestions on PRs)
- DependabotAutoMerge.yml (auto-merge Dependabot PRs)

Co-authored-by: ChrisRackauckas-Claude <accounts@chrisrackauckas.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 3 people

.github/workflows/DependabotAutoMerge.yml

@@ -0,0 +1,9 @@
+name: "Dependabot Auto-merge"
+on: pull_request
+permissions:
+  contents: write
+  pull-requests: write
+jobs:
+  automerge:
+    uses: "SciML/.github/.github/workflows/dependabot-automerge.yml@v1"
+    secrets: "inherit"

.github/workflows/RunicSuggestions.yml

@@ -0,0 +1,9 @@
+name: "Runic Suggestions"
+on: pull_request
+permissions:
+  contents: read
+  pull-requests: write
+jobs:
+  runic-suggestions:
+    uses: "SciML/.github/.github/workflows/runic-suggestions-on-pr.yml@v1"
+    secrets: "inherit"