refactor: rename to common/, clients/desktop, clients/wearos

Move three directories into their target topology:
- doctate-common/ -> common/
- client-desktop/ -> clients/desktop/
- watch/wearos/   -> clients/wearos/

Update doctate-common path-dependency in 3 Cargo.toml files
(server, clients/desktop, experiments) and the workspace
members list in the root Cargo.toml. Crate names unchanged
(doctate-server, doctate-common, doctate-desktop).

Workspace still in single-Cargo.lock form; isolation into
standalone workspaces follows in stage 3. All 508 tests pass,
experiments standalone-workspace also resolves the new path.

common/src/lib.rs

@@ -0,0 +1,18 @@
+pub mod ack;
+pub mod bulk;
+pub mod constants;
+pub mod oneliners;
+pub mod recordings;
+pub mod timestamp;
+pub mod url;
+
+pub use ack::{AckResponse, AckStatus};
+pub use bulk::{BulkAction, UnknownBulkAction};
+pub use constants::{
+    API_KEY_HEADER, CONTENT_TYPE_AUDIO_MP4, FIELD_AUDIO, FIELD_CASE_ID, FIELD_RECORDED_AT,
+    UPLOAD_PATH,
+};
+pub use oneliners::{ONELINER_FILENAME, ONELINERS_PATH, OnelinerEntry, OnelinersResponse};
+pub use recordings::{Loudness, RECORDING_META_SUFFIX, RecordingMeta, Transcript, TranscriptState};
+pub use timestamp::{filename_stem_to_recorded_at, now_rfc3339, recorded_at_to_filename_stem};
+pub use url::join_url;