ci: reduce noise and failed minutes in chronos check (#18)

* ci: add fast guards and path filters to chronos check

* ci: normalize chronos-check as paper-only workflow

Author: inaciovasquez2020

.github/workflows/chronos-check.yml

@@ -2,15 +2,31 @@ name: chronos-check
 
 on:
   push:
+    paths:
+      - ".github/workflows/chronos-check.yml"
+      - "**/*.tex"
+      - "**/*.md"
   pull_request:
+    paths:
+      - ".github/workflows/chronos-check.yml"
+      - "**/*.tex"
+      - "**/*.md"
 
 jobs:
   paper_only_check:
     runs-on: ubuntu-latest
     steps:
+      - name: Guard — lean-toolchain (optional, informational)
+        run: |
+          if [ -f lean-toolchain ]; then
+            echo "lean-toolchain present:"
+            cat lean-toolchain
+          else
+            echo "lean-toolchain not present — paper-only repo"
+          fi
+
       - name: Paper-only repository check
         run: |
           echo "Chronos-EntropyDepth is paper-only."
-          echo "No Lean or executable artifacts required."
+          echo "No Lean, Lake, or executable artifacts required."
           exit 0
-