Add CI unit tests, network health RPC, and fix checkpoint tests

- Add unit test build+run steps to both Qt and headless Linux CI jobs
- Enhance getnetworkinfo RPC with networkhealth object (peer mix, bootstrap mode, sync status)
- Rewrite Checkpoints_tests to validate actual chain checkpoints (0, 9000, 9001, 2186940)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/build-all.yml

@@ -147,6 +147,12 @@ jobs:
       - name: Build
         run: make -j$(nproc)
 
+      - name: Run unit tests
+        run: |
+          cd src
+          make -f makefile.unix test_triangles -j$(nproc)
+          ./test_triangles --log_level=test_suite
+
       - name: Strip binary
         run: strip --strip-all triangles-qt
 
@@ -183,6 +189,12 @@ jobs:
           mkdir -p obj
           make -f makefile.unix -j$(nproc)
 
+      - name: Run unit tests
+        run: |
+          cd src
+          make -f makefile.unix test_triangles -j$(nproc)
+          ./test_triangles --log_level=test_suite
+
       - name: Strip binary
         run: strip --strip-all src/trianglesd