docs: README — explain how analytics + Sessions enables unattended soak runs (#370)

The Analytics tier section opened with operational mechanics (sidecar
stack, ClickHouse, forwarder, retention) without spelling out the
load-bearing user benefit: **long unattended test runs**.

Adds a "Set it and forget it" lead paragraph that frames the workflow
explicitly — leave a session or a stack of grouped sessions running for
hours / overnight / across a weekend, come back the next day and triage
only the sessions the auto-classifier flagged as interesting. A
multi-day soak that would otherwise need a human watching turns into a
five-minute morning triage.

Names the three pieces that make this work:
- Forwarder writing every snapshot + HAR entry (no missed events)
- Auto-classifier flagging sessions with errors, frozen, segment stalls,
restarts, or 911 marks as \`interesting\`
- Picker's red-bar + chip cues making clean-vs-bad a visual scan rather
than a click-through

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: jonathaneoliver

README.md

@@ -306,6 +306,8 @@ The pattern is always: **change one variable per session, apply the same fault o
 
 ## Analytics tier
 
+**Set it and forget it.** With the analytics backend and the Sessions screens in place, the dashboard stops being a foreground-required watching tool and becomes a record-and-triage one. Leave a single Testing Session — or a stack of grouped sessions running a differential test — going for hours, overnight, across a weekend. The forwarder archives every snapshot and every HAR entry as they happen; the auto-classifier flags sessions that hit "really bad things" (errors, frozen, segment stalls, restarts, 911 marks) as `interesting`, the picker red-bars those rows, and 🚨 / ❄️ / ⛔ chips count the specific failures per session. When you come back, you don't replay every play that ran — you scan the picker for red bars and chip clusters, click into the handful that actually went sideways, and ignore the dozens that ran clean. A multi-day soak that would otherwise need a human watching turns into a five-minute morning triage.
+
 A sidecar stack (ClickHouse + Grafana + a small Go forwarder) auto-archives session metrics and per-request HAR for 30 days. Lives entirely under [`analytics/`](analytics/) — operationally independent of the live streaming path: if the forwarder dies, the live UI keeps working, archival just pauses until it restarts.
 
 | Component | Role |