feat(apiproxy): projection column on session.list — cold titles with zero log loads

SessionSummary grows an optional projections column (whole value per key,
same passthrough posture as the history-tail block): attached rows cut the
live registry watermark cache; cold rows view the persisted projection
cache's stored rows via the new registry viewCheckpoint face (version-
matching keys only, zero I/O) — the RFC's motivating scenario, every
session's title across a listing without loading one event log. The column
is fail-soft and absence-coded: no registry, no cache row, or a throwing
read serve the row without the column, never breaking the listing.

packages/host/apiproxy/tsconfig.json

@@ -35,6 +35,9 @@
     {
       "path": "../../session-projection/session-projection"
     },
+    {
+      "path": "../../session-projection/session-projection-cache"
+    },
     {
       "path": "../../skill/skill"
     },