OpenGL and Vulkan examples; ptr(int)/int(ptr); trailing commas in calls; drop .fn hint

- examples/opengl.fch: OpenGL 3.3 core, shaders, VAO/VBO, a spinning triangle (checked offscreen)
- examples/vulkan.fch: instance, GPUs with properties/memory/queues, logical device and queue
- ptr(n) and int(p) conversions for C APIs that pass offsets as pointers
- .ptr works on string literals; a comma after the last call argument is allowed
- a missing header included by an imported header is now named in the error
- the old .fn extension hint is gone (Finch is new, there are no old files)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/run.sh

@@ -38,7 +38,6 @@ for f in run/*.fch; do
 done
 
 for f in fail/*.fch; do
-    grep -q "^// expect:" "$f" || continue
     expect=$(head -1 "$f" | sed -n 's|^// expect: ||p')
     got=$("$FINCH" run "$f" < /dev/null 2>&1)
     status=$?