build: Digilent backend on by default on UNIX

The driver dlopen's libdjtg/libdmgr and degrades to "no probe" if
they're absent, so building it in has no cost or dependency.
BS_ENABLE_DIGILENT now defaults ON on UNIX (needs <dlfcn.h>); disable
with -DBS_ENABLE_DIGILENT=OFF. Docs updated; also fixes the quartiq
license note in CLAUDE.md (MIT, not BSD-2).

CMakeLists.txt

@@ -2,10 +2,17 @@ cmake_minimum_required(VERSION 3.10)
 
 project(BoundaryScanExplorer)
 
-# Optional backends. Off by default: no proprietary runtime dependency.
+# Digilent JTAG-SMT* backend. The driver dlopen's libdjtg/libdmgr at
+# runtime and degrades to "no probe" if they're absent, so building it
+# in costs nothing — default ON. Needs <dlfcn.h>, so UNIX only.
+if(UNIX)
+    set(BS_DIGILENT_DEFAULT ON)
+else()
+    set(BS_DIGILENT_DEFAULT OFF)
+endif()
 option(BS_ENABLE_DIGILENT
-       "Enable Digilent JTAG-SMT* backend (dlopen libdjtg.so / libdmgr.so at runtime; requires Adept Runtime installed)"
-       OFF)
+       "Enable Digilent JTAG-SMT* backend (dlopen libdjtg.so / libdmgr.so at runtime; Adept Runtime only needed to actually use such a probe)"
+       ${BS_DIGILENT_DEFAULT})
 
 # script and jtag_core must be the last linked archive for the application to compile
 set(BS_MODULES script jtag_core)