Keep the dense landmarks behind each eye reading, packed

The 106 points the eye boxes were cut from, stored beside the reading as
16-bit fixed point over the frame: 424 bytes a face, a seventh of a pixel
on a 6000-pixel frame, where f16 at the same size would have been six.
Derived data like the embedding, kept for the same reason — it cost a
fetch and a model run, and the next per-face pass should run from the
catalog. Shards carry it; a peer's shard from before it is still read.

docs/catalog.md

@@ -761,6 +761,10 @@ CREATE TABLE faces (
     eye_left_px     REAL,
     eye_left_sharp  REAL,
     sunglasses      REAL,
+    -- The 106 dense landmarks the eyes were read from, packed as 16-bit
+    -- fixed point over the frame: 424 bytes (schema V18). Kept so the next
+    -- per-face pass runs from the catalog rather than from the original.
+    landmarks_dense BLOB,
     -- Which model produced this. An embedding is only comparable to others
     -- from the same model; mixing them silently yields nonsense similarities.
     model_id   TEXT NOT NULL,