fix(ffi): correct field names in FFI functions

- formatrix_block_count: use doc.content instead of doc.blocks
- formatrix_get_format: use doc.source_format instead of doc.meta.source_format
- Mark FD-M10 (C FFI exports) as done in requirements

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: Jonathan D.A. Jewell

crates/formatrix-core/src/ffi.rs

@@ -278,7 +278,7 @@ pub unsafe extern "C" fn formatrix_block_count(handle: *const DocumentHandle) ->
     if handle.is_null() {
         return 0;
     }
-    (*handle).doc.blocks.len()
+    (*handle).doc.content.len()
 }
 
 /// Get the source format of a document
@@ -290,7 +290,7 @@ pub unsafe extern "C" fn formatrix_get_format(handle: *const DocumentHandle) ->
     if handle.is_null() {
         return FfiFormat::PlainText;
     }
-    (*handle).doc.meta.source_format.into()
+    (*handle).doc.source_format.into()
 }
 
 /// Free a document handle

docs/MOSCOW-REQUIREMENTS.adoc

@@ -55,7 +55,7 @@ This document defines Must/Should/Could requirements for each component of the d
 
 |FD-M10
 |C FFI exports for Ada TUI
-|🔲 Pending
+|✅ Done
 
 |FD-M11
 |Basic Ada TUI with ncurses