chat: bump simplexmq pin + document cross-table simplex_name discriminator

Pin bump 5ee014dd -> c9c2d19 picks up the 8 simplexmq commits since the
last bump (parseBare lowercase fix, forwarded-param cleanup, ServerTests
+ agent end-to-end tests, TldRegistries removal, SNRC ABI decoder,
NameRecord/NameOwner module extraction).

Adds a brief comment on clearConflictingContactProfileSimplexName_
explaining why the audit's flagged cross-table collision (between
contact_profiles.simplex_name and group_profiles.simplex_name) is
structurally impossible: SimplexNameInfo's strEncode prefixes contact
names with '@' and group names with '#', so the stored bytes never
overlap between the two tables.

Query-plan regen deferred (the test is non-deterministic in CI / dev
sandbox — see prior 6c990696c).

cabal.project

@@ -21,7 +21,7 @@ constraints: zip +disable-bzip2 +disable-zstd
 source-repository-package
     type: git
     location: https://github.com/simplex-chat/simplexmq.git
-    tag: 5ee014ddccd11e612fe873a7150ccf78b81a0ad2
+    tag: c9c2d19074a809ba505f393b41aa20ac7b437aa7
 
 source-repository-package
     type: git

src/Simplex/Chat/Store/Shared.hs

@@ -437,6 +437,11 @@ createContact db user profile = do
 -- row's display_name when a conflict was resolved, for the caller to surface
 -- as CEvtSimplexNameConflict. Newer-claim-wins matches RSLV semantics: the
 -- latest broadcast is the canonical assignment.
+--
+-- Cross-table collision with group_profiles.simplex_name is structurally
+-- impossible: strEncode SimplexNameInfo prefixes contact names with '@' and
+-- group names with '#', so the encoded bytes stored in the column never
+-- overlap between the two tables.
 clearConflictingContactProfileSimplexName_ :: DB.Connection -> UserId -> Maybe ProfileId -> Maybe SimplexNameInfo -> IO (Maybe ContactName)
 clearConflictingContactProfileSimplexName_ _ _ _ Nothing = pure Nothing
 clearConflictingContactProfileSimplexName_ db userId Nothing (Just simplexName) =