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>

docs/pl/dla-inzynierow.md

@@ -160,7 +160,7 @@ unary       = ( "-" | "!" | "~" ) unary | postfix ;
 postfix     = primary { "." IDENT [ args ] | "[" expr "]" } ;
 primary     = INT | FLOAT | STRING | CHAR | "true" | "false" | "null"
             | IDENT [ args ] | "(" expr ")" | "[" [ expr { "," expr } [","] ] "]" ;
-args        = "(" [ arg { "," arg } ] ")" ;  arg = [ IDENT ":" ] expr ;
+args        = "(" [ arg { "," arg } [","] ] ")" ;  arg = [ IDENT ":" ] expr ;
 ```
 
 **Koniec instrukcji.** Po instrukcji `endOfStatement()` wymaga `}`, końca pliku albo tokenu
@@ -347,6 +347,7 @@ Nie ma promocji całkowitych z C: `u8 + u8` zostaje `u8`.
 | `[]u8`/`[]char` → str | `finch_str_from_bytes` |
 | ptr → str | `finch_str_from_c` (pożyczony, `cap = -1`) |
 | ptr ↔ ptr | nic |
+| int → ptr / ptr → int | `inttoptr` / `ptrtoint` |
 
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