feat(dashboard): LLM stats answer who/what spends tokens — member scope chips and spend breakdowns

The stats section was designed single-user: four global charts, no
attribution. Request metadata rows now carry the session's source and
the frame's agent_id/depth (additive ensure_column), denormalized at log
time by the LoggingModel from the owner's pool — off the turn's hot
path, degrading to NULLs, never to a lost row.

The dashboard gains member scope chips filtering every chart, and a
breakdown row splitting the range's billed tokens by member, kind
(chat / sub-agents / cron / system agents / channels), agent, model and
provider — a sub-agent's spend is attributed to the sub-agent itself.
Rows predating the columns group under 'older data'.

web/css/home.css

@@ -312,6 +312,24 @@ dashboard-page {
   color: #fff;
 }
 
+/* Scope chips (member filter) — same pill look as the range buttons. */
+.home-stats-scope {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 6px;
+  margin: -0.25rem 0 1rem;
+}
+
+/* Subsection label above the breakdown grid. */
+.home-stats-sub {
+  font-size: 0.78rem;
+  font-weight: 600;
+  color: var(--bs-secondary-color);
+  text-transform: uppercase;
+  letter-spacing: 0.04em;
+  margin: 0.25rem 0 0.75rem;
+}
+
 .home-stats-loading,
 .home-stats-empty {
   display: flex;
@@ -325,7 +343,7 @@ dashboard-page {
 
 .home-stats-grid {
   display: grid;
-  grid-template-columns: 1fr 1fr;
+  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
   gap: 1rem;
   margin-bottom: 2rem;
 }