refactor: require external Gemma 2 and GPT-OSS tokenizers (#1974)

include/stable-diffusion.h

@@ -244,7 +244,7 @@ typedef struct {
     bool disable_segmented_compute;  // Force monolithic graph execution even when automatic graph cutting would fit memory better
     float linear_scale;              // Override linear input scaling; 0 keeps the model default
     float attn_scale;                // Override flash-attention K/V scaling; 0 keeps the model default
-    const char* tokenizer;           // Optional tokenizer.json path or main=FILE,clip-l=FILE,clip-g=FILE assignments
+    const char* tokenizer;           // tokenizer.json path or main=FILE,clip-l=FILE,clip-g=FILE assignments; required for PiD and Lens
 } sd_ctx_params_t;
 
 typedef struct {