Vendor WildCat 4 SDK as src/wc_sdk/, add to fpc.cfg search path

docs/format-notes/dependencies.md

@@ -22,14 +22,14 @@ Plan:
 
 ## ma.fmt.wildcat.pas + ma.fmt.wcutil.pas
 
-Currently use the WildCat SDK (`WcType`, `WcMsgDb`, `WcUserDb`, `WcGlobal`,
-`WcMisc`, `WcDb`, `Os2Comp`, `DosUtil`, `p_System`).
+Use the WildCat 4 SDK. The SDK source has been copied verbatim into
+`src/wc_sdk/` (formerly `wc_dev/` in Allfix) so this repo can build the
+Wildcat backend without external paths.
 
-Plan:
-- Treat the WC SDK as an optional dependency. Wrap the entire backend in
-  `{$IFDEF WILDCAT4}` so builds without the SDK still link.
-- Document in `README.md` that Wildcat support requires the WC SDK source
-  on the FPC search path.
+The SDK pulls in OS/2-era helpers (`Os2Comp`, `DosUtil`, `p_System`,
+`btisbase`, `isamtool`, …). Keeping it on its own search-path entry
+(`-Fusrc/wc_sdk`) means callers that don't need Wildcat can omit the
+backend without forcing the SDK onto the build line.
 
 ## include.inc