Deduplicate cJSON: consolidate 4 copies into a single canonical pair

- Compile cJSON.c as a standalone C translation unit (added stdbool.h)
- Rename hush_cJSON.c → hush_cJSON.cpp and compile as standalone C++ unit
  with forward declarations for external deps (_stripwhite, clonestr, etc.)
- Remove #include "cJSON.c" unity-build from hush_cJSON
- Change hush.h from #include "hush_cJSON.c" to #include "hush_cJSON.h"
- Add both files to libbitcoin_server_a_SOURCES in Makefile.am
- Delete cc/dapps/cJSON.c (old 2009 fork, 1201 lines removed)
- Replace cc/includes/cJSON.h with thin redirect to canonical headers
- Update dapp includes to reference canonical cJSON.c

doc/codebase-cleanup.md

@@ -83,14 +83,14 @@ There are **13,652 lines** of implementation code in `hush_*.h` headers:
 
 ## 6. Deduplicate Vendored Code
 
-`cJSON` exists in **4 copies**:
+`cJSON` has been consolidated:
 
-- `src/cJSON.c` + `src/cJSON.h`
-- `src/hush_cJSON.c` + `src/hush_cJSON.h`
-- `src/cc/dapps/cJSON.c`
-- `src/cc/includes/cJSON.h`
+- `src/cJSON.c` + `src/cJSON.h` — canonical implementation, compiled as a standalone C translation unit
+- `src/hush_cJSON.cpp` + `src/hush_cJSON.h` — helper/wrapper functions, compiled as a standalone C++ translation unit
+- `src/cc/includes/cJSON.h` — thin redirect to the canonical headers above
+- `src/cc/dapps/cJSON.c` — deleted (old 2009 fork); dapp includes updated to use canonical copy
 
-- [ ] Consolidate to a single copy and have other modules link against it
+- [x] Consolidate to a single copy and have other modules link against it
 
 ## 7. Relocate Shell Scripts Out of `src/`