feat(faces): domain entities, ports & no-op analyzer

Phase 2 increment 2:
- domain: Face, Person, BoundingBox, DetectedFace (512-d embeddings).
- ports: FaceAnalyzerPort (detect + embed from raw bytes; decodes internally
  so the application layer stays image/ML-crate agnostic) and FaceRepository
  (user-scoped face/person persistence).
- DTOs: PersonDto, FaceBoxDto.
- NoopFaceAnalyzer — reports is_ready()==false and returns no faces, so the
  whole People pipeline compiles and runs inert until the operator wires a
  real ONNX-backed analyzer.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JW6ghFMDtnRYuYNzZhb47M

src/application/dtos/mod.rs

@@ -14,6 +14,7 @@ pub mod geo_dto;
 pub mod grant_dto;
 pub mod i18n_dto;
 pub mod pagination;
+pub mod people_dto;
 pub mod playlist_dto;
 pub mod plugin_dto;
 pub mod recent_dto;

src/application/dtos/people_dto.rs

@@ -0,0 +1,30 @@
+//! DTOs for the People (faces) API.
+
+use serde::Serialize;
+use utoipa::ToSchema;
+
+/// A named (or unnamed) identity cluster, with a cover photo for its tile.
+#[derive(Debug, Clone, Serialize, ToSchema)]
+pub struct PersonDto {
+    pub id: String,
+    /// `None` until the user names the person.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub name: Option<String>,
+    /// File id of the cover face's photo, for the tile thumbnail.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub cover_file_id: Option<String>,
+    pub face_count: i64,
+    pub is_hidden: bool,
+}
+
+/// One face box within a photo (for tagging overlays in the lightbox).
+#[derive(Debug, Clone, Serialize, ToSchema)]
+pub struct FaceBoxDto {
+    pub id: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub person_id: Option<String>,
+    pub x: f32,
+    pub y: f32,
+    pub w: f32,
+    pub h: f32,
+}