ci: bump Zig to 0.16.0 and update README requirement

Matches minimum_zig_version bump in build.zig.zon for v0.5.0 release.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: zlice dev

.github/workflows/ci.yml

@@ -18,8 +18,8 @@ jobs:
 
       - name: Install Zig
         run: |
-          curl -sL "https://ziglang.org/download/0.15.2/zig-x86_64-linux-0.15.2.tar.xz" | tar -xJ
-          echo "$PWD/zig-x86_64-linux-0.15.2" >> "$GITHUB_PATH"
+          curl -sL "https://ziglang.org/download/0.16.0/zig-x86_64-linux-0.16.0.tar.xz" | tar -xJ
+          echo "$PWD/zig-x86_64-linux-0.16.0" >> "$GITHUB_PATH"
 
       - name: Install dependencies
         run: |

README.md

@@ -111,7 +111,7 @@ zephwm/
 
 ## Building
 
-Requires **Zig 0.15.0+** and the following system libraries:
+Requires **Zig 0.16.0+** and the following system libraries:
 
 ```
 xcb xcb-randr