faces: phase 2 — schema + manual face/person CRUD

Land the persistence model and HTTP surface for local face recognition.
Inference still lives in Apollo (Phase 1); this side adds the data home
plus every endpoint Apollo's UI and FileViewer-React will consume.

Schema (new migration 2026-04-29-000000_add_faces):
  - persons: visual identities. Optional entity_id bridges to the
    existing knowledge-graph entities table; auto-bridging is left to
    the management UI (we don't muddy LLM provenance from face rows).
    UNIQUE(name COLLATE NOCASE) so 'alice' / 'Alice' fold to one row.
  - face_detections: keyed on content_hash (cross-library dedup), with
    status='detected' carrying bbox + 512-d embedding BLOB, and
    'no_faces' / 'failed' marker rows that tell Phase 3's file watcher
    not to re-scan. Marker invariant enforced via CHECK; partial UNIQUE
    on content_hash WHERE status='no_faces' guards against double-marks.

Schema regenerated with `diesel print-schema` against a clean migration
run; joinables added for face_detections → libraries / persons and
persons → entities.

face_client.rs (sibling of apollo_client.rs):
  - reqwest multipart, 60 s timeout (CPU inference on a backlog can be
    slow; bounded threadpool on Apollo serializes calls anyway).
  - FaceDetectError::{Permanent, Transient, Disabled} — Phase 3 keys
    its marker-row decision on this. 422 → mark failed, 5xx → defer.
  - APOLLO_FACE_API_BASE_URL falls back to APOLLO_API_BASE_URL when
    unset; both unset = is_enabled() false, callers no-op.

faces.rs (DAO + handlers):
  - SqliteFaceDao implements the full FaceDao trait; person face counts
    go through sql_query because diesel's BoxedSelectStatement +
    group_by trips trait-resolver recursion.
  - merge_persons re-points face rows in a transaction, copies notes
    when target's are empty, deletes src.
  - manual POST /image/faces resolves content_hash through image_exif,
    crops the user-drawn bbox with 10% padding (detector wants context
    around ears/jaw), POSTs the crop to face_client.embed for a real
    ArcFace vector, then inserts source='manual'.
  - Cluster-suggest (Phase 6) gets its data from
    GET /faces/embeddings — base64-encoded paged BLOBs so Apollo's
    DBSCAN can stream them without ImageApi pre-aggregating.

Endpoints registered alongside add_*_services in main.rs:
  GET    /faces/stats?library=
  GET    /faces/embeddings?library=&unassigned=&limit=&offset=
  GET    /image/faces?path=&library=
  POST   /image/faces                        (manual create via embed)
  PATCH  /image/faces/{id}
  DELETE /image/faces/{id}
  GET    /persons?library=
  POST   /persons
  GET    /persons/{id}
  PATCH  /persons/{id}
  DELETE /persons/{id}?cascade=set_null|delete   (set_null default)
  POST   /persons/{id}/merge
  GET    /persons/{id}/faces?library=

The file-watch hook (Phase 3) and the rerun-on-one-photo handler
(Phase 6) live behind the FaceDao methods marked dead_code today —
they're called only when those phases land. Same shape for the trait
methods that aren't reached by Phase 2 routes.

Tests: 3 DAO unit tests cover person CRUD + case-insensitive uniqueness,
marker-row idempotency (mark_status is a no-op when any row exists),
and merge re-pointing faces.

Cargo.toml: reqwest gains the `multipart` feature.

cargo build / cargo test --lib / cargo fmt / cargo clippy --all-targets
all clean for the new code; the two pre-existing test_path_excluder
failures and the pre-existing sort_by clippy warnings are unrelated and
present on master.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

migrations/2026-04-29-000000_add_faces/up.sql

@@ -0,0 +1,67 @@
+-- Local face recognition tables.
+--
+-- `persons` are visual identities (the "who" of a face). The optional
+-- `entity_id` bridges to the existing knowledge graph `entities` table —
+-- when set, this person is the visual side of an LLM-extracted entity.
+-- Don't auto-create entities from persons; the entity table represents
+-- LLM-extracted knowledge with its own confidence semantics, and silently
+-- filling it from face detections muddies the provenance.
+--
+-- `face_detections` carries one row per detected face on a content_hash,
+-- plus marker rows with `status='no_faces'` or `status='failed'` so the
+-- file watcher knows not to re-scan a hash. Keying on `content_hash`
+-- (cross-library dedup) rather than `(library_id, rel_path)` means the
+-- same JPEG in two libraries is scanned once. The denormalized `rel_path`
+-- carries the most-recently-seen path — useful for cluster-thumb URL
+-- generation; canonical path lookup goes through image_exif.
+
+CREATE TABLE persons (
+    id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
+    name TEXT NOT NULL,
+    cover_face_id INTEGER,                  -- backfilled when the first face binds
+    entity_id INTEGER,                      -- optional bridge to entities(id)
+    created_from_tag BOOLEAN NOT NULL DEFAULT 0,
+    notes TEXT,
+    created_at BIGINT NOT NULL,
+    updated_at BIGINT NOT NULL,
+    CONSTRAINT fk_persons_entity FOREIGN KEY (entity_id) REFERENCES entities(id) ON DELETE SET NULL,
+    UNIQUE(name COLLATE NOCASE)
+);
+
+CREATE INDEX idx_persons_entity ON persons(entity_id);
+
+CREATE TABLE face_detections (
+    id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
+    library_id INTEGER NOT NULL,
+    content_hash TEXT NOT NULL,             -- canonical key (cross-library dedup)
+    rel_path TEXT NOT NULL,                 -- denormalized; most recently seen
+    bbox_x REAL,                            -- normalized 0..1; NULL on marker rows
+    bbox_y REAL,
+    bbox_w REAL,
+    bbox_h REAL,
+    embedding BLOB,                         -- 512×f32 = 2048 bytes; NULL on marker rows
+    confidence REAL,                        -- detector score
+    source TEXT NOT NULL,                   -- 'auto' | 'manual'
+    person_id INTEGER,
+    status TEXT NOT NULL DEFAULT 'detected', -- 'detected' | 'no_faces' | 'failed'
+    model_version TEXT NOT NULL,            -- e.g. 'buffalo_l'; embedding lineage
+    created_at BIGINT NOT NULL,
+    CONSTRAINT fk_fd_library FOREIGN KEY (library_id) REFERENCES libraries(id),
+    CONSTRAINT fk_fd_person FOREIGN KEY (person_id) REFERENCES persons(id) ON DELETE SET NULL,
+    -- Detected rows carry geometry + embedding; marker rows ('no_faces',
+    -- 'failed') carry neither. CHECK enforces the invariant so manual
+    -- inserts can't slip through with half a row.
+    CONSTRAINT chk_marker CHECK (
+        (status = 'detected' AND bbox_x IS NOT NULL AND embedding IS NOT NULL)
+        OR (status IN ('no_faces','failed') AND bbox_x IS NULL AND embedding IS NULL)
+    )
+);
+
+CREATE INDEX idx_face_detections_hash       ON face_detections(content_hash);
+CREATE INDEX idx_face_detections_lib_path   ON face_detections(library_id, rel_path);
+CREATE INDEX idx_face_detections_person     ON face_detections(person_id);
+CREATE INDEX idx_face_detections_status     ON face_detections(status);
+-- One marker row per (content_hash, status='no_faces') so the file watcher
+-- doesn't double-mark when a hash is seen on multiple full-scan passes.
+CREATE UNIQUE INDEX idx_face_detections_no_faces_unique
+    ON face_detections(content_hash) WHERE status = 'no_faces';