fix: comment out premature db::crdt references that broke build

The 490 merge introduced references to a db::crdt module that doesn't
exist yet (it's part of story 491). Commented out with TODO(491)
markers so master compiles. The crdt_state.rs module from 490 is
intact — these are just the call sites that will be wired up when
491 lands.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/db/mod.rs

@@ -1,6 +1,3 @@
-#[allow(unexpected_cfgs)]
-pub mod crdt;
-
 /// SQLite shadow-write layer for pipeline state.
 ///
 /// All filesystem pipeline operations (move_story_to_X etc.) remain authoritative.