feat: Add doctate-client-core crate

Introduces a new crate `doctate-client-core` to house shared client-side
logic. This includes:

- `case_store`: Manages local case marker files and merging with server
  snapshots.
- `snapshot_cache`: Placeholder for caching server responses.
- `oneliner_poller`: Placeholder for the background polling task.

The workspace configuration and `Cargo.lock` have been updated to
include the new crate.

doctate-common/src/lib.rs

@@ -1,5 +1,6 @@
 pub mod ack;
 pub mod constants;
+pub mod oneliners;
 pub mod timestamp;
 
 pub use ack::{AckResponse, AckStatus};
@@ -7,4 +8,5 @@ pub use constants::{
     API_KEY_HEADER, CONTENT_TYPE_AUDIO_MP4, FIELD_AUDIO, FIELD_CASE_ID, FIELD_RECORDED_AT,
     UPLOAD_PATH,
 };
+pub use oneliners::{OnelinerEntry, OnelinersResponse, ONELINERS_PATH};
 pub use timestamp::{filename_stem_to_recorded_at, now_rfc3339, recorded_at_to_filename_stem};

doctate-common/src/oneliners.rs

@@ -0,0 +1,32 @@
+//! Shared DTOs for the `/api/oneliners` endpoint.
+//!
+//! Server serializes [`OnelinersResponse`]; clients deserialize the same
+//! type. Keeping this in a client-agnostic crate avoids drift between
+//! server output and client parsing.
+
+use serde::{Deserialize, Serialize};
+
+/// HTTP path of the oneliners endpoint.
+pub const ONELINERS_PATH: &str = "/api/oneliners";
+
+/// Full response body of `GET /api/oneliners`.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OnelinersResponse {
+    /// RFC3339 UTC timestamp at which the server built this response.
+    pub as_of: String,
+    /// Effective window (after server-side clamp).
+    pub window_hours: u32,
+    /// Oneliners of cases whose earliest recording sits inside the window,
+    /// sorted newest-first by `created_at`.
+    pub oneliners: Vec<OnelinerEntry>,
+}
+
+/// One case summary. `oneliner` is `None` while the case is still
+/// transcribing / generating; `updated_at` is `None` for the same reason.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OnelinerEntry {
+    pub case_id: String,
+    pub oneliner: Option<String>,
+    pub created_at: String,
+    pub updated_at: Option<String>,
+}