docs(rust): refresh migration boundary notes

Keep the migration map aligned with the completed adaptive-refresh and window
overflow seams. The CLI description now identifies only the remaining C
progression and diagnostic callbacks, and the compression description records
that Rust owns the stateful window rebase. The explicit list of private C
layout and callback boundaries remains unchanged so the hybrid build is not
mistaken for a finished rewrite.

Test Plan:
- git diff --cached --check

rust/README.md

@@ -54,8 +54,8 @@ zstd ABI:
     direct versus buffered output, pending-output draining, and frame reset
     policy. The external-sequence-and-literals block loop and public sequence
     conversion are Rust-owned as well; Rust also owns overflow-correction
-    branch/order while C retains the private window, workspace, and index
-    callbacks and only CCtx-facing adapters.
+    branch/order and the window rebase while C retains private workspace and
+    index callbacks plus CCtx-facing adapters.
   - `zstd_compress_frame` serializes frame headers, skippable frames, and the
     last empty block; it takes scalar frame parameters so the C-owned
     `ZSTD_CCtx_params` layout never crosses the language boundary.
@@ -143,7 +143,7 @@ zstd ABI:
     so library builds do not acquire program-only dependencies.  The C
     `fileio` layer retains the format-specific codec callbacks, private
     asynchronous-pool adapters, metadata, zstd codec/error mapping, and the
-    adaptive clock/progression and diagnostic callbacks, while Rust owns the
+    adaptive progression and diagnostic callbacks, while Rust owns the
     mixed-format probe/dispatch
     loop, zstd stream-compression I/O loop, scalar adaptive decisions,
     optional-format decompression loops, decompression result policy/final
@@ -207,8 +207,8 @@ scalar CCtx-reset plan, post-match-state storage reservation order, and
 match-state reset policy/order for both CCtx and CDict; C retains
 private layout-size inputs, workspace resize/layout, private field publication,
 and allocator callbacks. Private CCtx reset/matchfinder/workspace operations
-and codec/adaptive clock, progression-snapshot, and diagnostic callbacks remain
-in C. CDict initialization ordering and scalar publication,
+and codec, progression-snapshot, and diagnostic callbacks remain in C. Rust
+owns adaptive refresh timing. CDict initialization ordering and scalar publication,
 shared compression-begin dictionary selection, CDict reset attach-versus-copy
 selection, and CDict-begin parameter selection, initialization ordering, and
 source-window policy now run in Rust behind private-state bridges; their C