ci: bump actions to current majors and add CI badge to README

actions/checkout v5 → v6 and actions/upload-artifact v5 → v7. The
previous v5 bump left upload-artifact on a Node.js 20 release that
GitHub will force-migrate to Node.js 24 on 2026-06-02; the v7 line is
already on Node.js 24 and clears the deprecation annotation. checkout
v6 is the matching current major.

README gets a top-of-page CI badge that links to the workflow page
and turns red on the first failing run on main.

Author: satyanar-lab

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
     name: Host unit tests
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Build and run tests
         working-directory: tests
         run: |
@@ -35,7 +35,7 @@ jobs:
       ASAN_OPTIONS: detect_leaks=1:halt_on_error=1:abort_on_error=1
       UBSAN_OPTIONS: halt_on_error=1:abort_on_error=1:print_stacktrace=1
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Build with sanitizers and run
         working-directory: tests
         run: |
@@ -58,7 +58,7 @@ jobs:
     name: Static analysis (cppcheck)
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Install cppcheck
         run: sudo apt-get update && sudo apt-get install -y cppcheck
       - name: Run cppcheck on application sources
@@ -76,7 +76,7 @@ jobs:
     name: Firmware cross-compile (arm-none-eabi-gcc)
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Install ARM GCC toolchain
         run: sudo apt-get update && sudo apt-get install -y gcc-arm-none-eabi
       - name: Build bcm_master
@@ -90,7 +90,7 @@ jobs:
           arm-none-eabi-size bcm_master/build/bcm_master.elf
           arm-none-eabi-size lighting_node/build/lighting_node.elf
       - name: Upload firmware artifacts
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v7
         with:
           name: firmware-images
           path: |

README.md

@@ -1,5 +1,7 @@
 # Two-Node BCM Control System
 
+[![CI](https://github.com/satyanar-lab/Two-Node-BCM-Control-System/actions/workflows/ci.yml/badge.svg?branch=main)](https://github.com/satyanar-lab/Two-Node-BCM-Control-System/actions/workflows/ci.yml)
+
 An embedded C project demonstrating a two-node Body Control Module (BCM) system
 communicating over CAN FD. One node reads physical switches and acts as the
 bus master; the other drives lighting outputs based on received commands.