build: capnweb as a git submodule (ryanrasti/capnweb @ generalize_record_replay)

packages/capnweb un-gitignored and registered as a submodule pinned at
efebddf (getLocalTarget tip of the record-replay closure branch);
package-lock picks up the file: dependency.

NOTE: the fork's generalize_record_replay is pushed only through
43dc308 — the top 4 commits (sync replay, zero-arg closures, RpcStub
import fix, getLocalTarget) need a `git push` from packages/capnweb
before anyone else can clone this pin.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: ryanrasti

.gitignore

@@ -11,5 +11,4 @@ site/public/api/
 site/public/demo.ts.static
 site/public/typegres.js
 site/public/typegres.d.ts
-packages/
 .claude/

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "packages/capnweb"]
+	path = packages/capnweb
+	url = https://github.com/ryanrasti/capnweb.git