Fix the ktlint and compat-test failures, and start using the Rust gate

Two more from the step-2 removals:

**Two unused Kotlin imports** — `FilterChip` (the Note/List switch) and
`Icons.Filled.Create` (the "switch to a note" icon), both orphaned when their
callers went. ktlint treats them as errors.

**`server_info_tolerates_unknown_and_absent_fields`** pinned
`sync_protocol_version: 1` as a literal, so bumping the protocol to v2 made it
fail for a reason that has nothing to do with what it tests. It is about unknown
FIELDS; the versions now come from `CLIENT_PROTOCOL_VERSION`, like every other
test in that file already did.

The bigger fix is the habit. `ci-requirements.md` has documented since
2026-08-18 that the operator authorised running fmt/clippy/test against the CI
image locally, and I had not been doing it. All three now pass here — 116 tests,
clippy clean, fmt clean — and every Rust failure in this milestone so far would
have been caught by them in under a minute instead of by CI, several commits
downstream. Noted in ci-requirements so the next session doesn't relearn it: a
removal is exactly the change that looks too safe to check.

android/app/src/main/java/com/fabledsword/thoughtsync/ui/ComposeSheet.kt

@@ -9,7 +9,6 @@ import androidx.compose.foundation.layout.navigationBarsPadding
 import androidx.compose.foundation.layout.padding
 import androidx.compose.material3.Button
 import androidx.compose.material3.ExperimentalMaterial3Api
-import androidx.compose.material3.FilterChip
 import androidx.compose.material3.ModalBottomSheet
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton

android/app/src/main/java/com/fabledsword/thoughtsync/ui/EditorChrome.kt

@@ -14,7 +14,6 @@ import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.automirrored.filled.List
 import androidx.compose.material.icons.filled.Close
-import androidx.compose.material.icons.filled.Create
 import androidx.compose.material.icons.filled.MoreVert
 import androidx.compose.material.icons.filled.Notifications
 import androidx.compose.material3.BottomAppBar