docs(fork-c/S0): correct two doc-accuracy lines (base-equivalence wording + grounded FFI count)

attempt-2 review fixes (docs-only; contract mechanics confirmed sound):
- README + S0.2 grep-clean: 'S0 HEAD == base' / 'S0 == base' were inaccurate
  (HEAD carries the docs/examples/tests diff). Reword to: production/compiler
  behavior is base-equivalent — zero src/ changes, single-author output
  byte-identical to base by construction — HEAD is a distinct commit, not base.
- S0.3 ledger: drop the stale '116-class corpus' FFI wording for the grounded
  live count (96 entry trees / 95 active markers), matching the S0.1 count note.

No partition / manifest / examples / harness change. Gate green:
zig build + zig build test (LSP sweep 574, no crash) + run_examples (540/0);
m3te ios-sim build via main binary exit 0.

docs/fork-c/README.md

@@ -21,7 +21,10 @@ tree would not be committed; the S0 contract must be committed. `docs/` is track
 - **Base:** `wt-stdlib-base @ 1f755284d98c6e8ebba953045c06e35d8cbe6278` (A–E6a merged).
 - **E6b:** `flow/stdlib/E6b @ af737b0` — PAUSED, **unmerged**, all transitional, destined
   for S3/S6 deletion. Its semantics goldens are harvested; its src is never merged.
-- **This branch:** `flow/stdlib/S0` (branched from the base; S0 HEAD == base).
+- **This branch:** `flow/stdlib/S0` (branched from the base). **Production/compiler
+  behavior is base-equivalent** — zero `src/` changes, single-author output
+  byte-identical to base by construction — but S0 HEAD is a distinct commit carrying
+  the docs/examples/tests diff (it does **not** equal base).
 
 ## Contents