libghostty: add hyperlink URI accessor to grid_ref API

Add ghostty_grid_ref_hyperlink_uri to extract the OSC 8 hyperlink
URI from a cell at a grid reference position. Follows the same
buffer pattern as ghostty_grid_ref_graphemes: callers pass a buffer
and get back the byte length, or GHOSTTY_OUT_OF_SPACE with the
required size if the buffer is too small. Cells without a hyperlink
return success with length 0.

include/ghostty/vt/grid_ref.h

@@ -109,6 +109,32 @@ GHOSTTY_API GhosttyResult ghostty_grid_ref_graphemes(const GhosttyGridRef *ref,
                                          size_t buf_len,
                                          size_t *out_len);
 
+/**
+ * Get the hyperlink URI for the cell at the grid reference's position.
+ *
+ * Writes the URI bytes into the provided buffer. If the cell has no
+ * hyperlink, out_len is set to 0 and GHOSTTY_SUCCESS is returned.
+ *
+ * If the buffer is too small (or NULL), the function returns
+ * GHOSTTY_OUT_OF_SPACE and writes the required number of bytes to
+ * out_len. The caller can then retry with a sufficiently sized buffer.
+ *
+ * @param ref Pointer to the grid reference
+ * @param buf Output buffer for the URI bytes (may be NULL)
+ * @param buf_len Size of the output buffer in bytes
+ * @param[out] out_len On success, the number of bytes written. On
+ *             GHOSTTY_OUT_OF_SPACE, the required buffer size in bytes.
+ * @return GHOSTTY_SUCCESS on success, GHOSTTY_INVALID_VALUE if the ref's
+ *         node is NULL, GHOSTTY_OUT_OF_SPACE if the buffer is too small
+ *
+ * @ingroup grid_ref
+ */
+GHOSTTY_API GhosttyResult ghostty_grid_ref_hyperlink_uri(
+    const GhosttyGridRef *ref,
+    uint8_t *buf,
+    size_t buf_len,
+    size_t *out_len);
+
 /**
  * Get the style of the cell at the grid reference's position.
  *