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/domain/entities/face.rs

@@ -0,0 +1,72 @@
+//! Domain entities for the People (faces) feature.
+
+use chrono::{DateTime, Utc};
+use uuid::Uuid;
+
+/// Length of a face embedding vector (ArcFace-style).
+pub const EMBEDDING_DIM: usize = 512;
+
+/// A face bounding box in normalized image coordinates (each component 0..1).
+#[derive(Debug, Clone, Copy)]
+pub struct BoundingBox {
+    pub x: f32,
+    pub y: f32,
+    pub w: f32,
+    pub h: f32,
+}
+
+impl BoundingBox {
+    /// `[x, y, w, h]` — the storage representation (Postgres `REAL[]`).
+    pub fn to_array(self) -> Vec<f32> {
+        vec![self.x, self.y, self.w, self.h]
+    }
+
+    /// Build from a stored `[x, y, w, h]` array; missing components default to 0.
+    pub fn from_slice(a: &[f32]) -> Self {
+        Self {
+            x: a.first().copied().unwrap_or(0.0),
+            y: a.get(1).copied().unwrap_or(0.0),
+            w: a.get(2).copied().unwrap_or(0.0),
+            h: a.get(3).copied().unwrap_or(0.0),
+        }
+    }
+}
+
+/// A face produced by the analyzer but not yet persisted: where it is, how
+/// confident the detector was, an optional quality score, and a 512-d,
+/// L2-normalized embedding.
+#[derive(Debug, Clone)]
+pub struct DetectedFace {
+    pub bbox: BoundingBox,
+    pub det_score: f32,
+    pub quality: Option<f32>,
+    pub embedding: Vec<f32>,
+}
+
+/// A persisted face detection.
+#[derive(Debug, Clone)]
+pub struct Face {
+    pub id: Uuid,
+    pub file_id: Uuid,
+    pub user_id: Uuid,
+    /// Identity cluster this face belongs to, if any.
+    pub person_id: Option<Uuid>,
+    pub bbox: BoundingBox,
+    pub det_score: f32,
+    pub quality: Option<f32>,
+    pub embedding: Vec<f32>,
+    pub blob_hash: Option<String>,
+    pub created_at: DateTime<Utc>,
+}
+
+/// An identity cluster ("person"). `display_name` is `None` until the user
+/// names it.
+#[derive(Debug, Clone)]
+pub struct Person {
+    pub id: Uuid,
+    pub user_id: Uuid,
+    pub display_name: Option<String>,
+    pub cover_face_id: Option<Uuid>,
+    pub is_hidden: bool,
+    pub created_at: DateTime<Utc>,
+}

src/domain/entities/mod.rs

@@ -4,6 +4,7 @@ pub mod calendar_event;
 pub mod contact;
 pub mod device_code;
 pub mod entity_errors;
+pub mod face;
 pub mod file;
 pub mod folder;
 pub mod magic_link_token;