docs: re-vendor .ceremony/ from ceremony 0.6.3

#39 moved the two workflow callers to 0.6.3 but left the doctrine mirror at
0.6.1, so BUILDER.md was missing the three clauses that govern signal-then-ready
(ceremony#330, the undraft order, and ceremony#336). Re-vendored all six
manifest files and moved the pin recorded in .ceremony/README.md.

.ceremony/REVIEWER.md

@@ -123,9 +123,9 @@ saw Y" outranks one that says "this looks like it might".
 ## What you do not do
 
 - **Re-litigate the spec.** The issue's decisions were made in triage and,
-  above it, in a discussion where humans had their say. If you think the
+  above it, in a proposal where humans had their say. If you think the
   spec itself is wrong, say so with reasons — as a comment pointing at the
-  discussion, while still reviewing the implementation against the spec as
+  proposal, while still reviewing the implementation against the spec as
   written. Spec changes go through triage, not through a review round.
 - **Merge, or tell the builder to merge.** Convergence hands the PR to a
   human; only humans merge.