## Summary
Sessions started from the agent Test playground were tagged with a
`"playground"` tag that rendered in the Sessions table's Tags column.
They are now flagged with a real `Session.isTest` boolean (mirroring
`TaskRun.isTest`) and surfaced as a dedicated **Test** column with a
check icon, to the left of Tags, on both the Sessions page and the Agent
landing page, plus a matching **Test** property on the session detail
page. This mirrors how Standard and Scheduled task runs already indicate
test runs.
## Design
`isTest` is a new `Session` column (Postgres) replicated into ClickHouse
`sessions_v1` alongside the existing fields. The Sessions list reads
`isTest` from Postgres for display (ClickHouse only supplies the ordered
session IDs), so the column renders correctly without a ClickHouse
backfill.
The playground action now sets `isTest: true` on session create instead
of writing the `"playground"` tag. The triggered run still carries
`playground:true` in its own tags (unchanged). A migration backfills
existing sessions, setting `isTest = true` and stripping the
now-redundant `"playground"` tag where it is present, so the list and
detail views render consistently without read-time tag filtering.
James Ritchie
a90a495542