store: migration 0023 host_repo_stats_history

internal/store/migrations/0023_host_repo_stats_history.sql

@@ -0,0 +1,19 @@
+-- 0023_host_repo_stats_history.sql
+--
+-- Daily time-series of per-host repo metrics, used by the P6-03
+-- trend sparkline + chart. One row per (host_id, UTC date),
+-- last-write-wins per column. Population is best-effort and
+-- piggy-backs on the existing repo.stats WS message — nothing
+-- else writes here.
+
+CREATE TABLE host_repo_stats_history (
+  host_id           TEXT NOT NULL REFERENCES hosts(id) ON DELETE CASCADE,
+  day               TEXT NOT NULL,           -- 'YYYY-MM-DD' UTC
+  total_size_bytes  INTEGER,                 -- nullable: partial patches preserve existing value
+  snapshot_count    INTEGER,                 -- nullable
+  recorded_at       TEXT NOT NULL,           -- RFC3339Nano of latest write
+  PRIMARY KEY (host_id, day)
+);
+
+CREATE INDEX host_repo_stats_history_host_day
+  ON host_repo_stats_history(host_id, day DESC);