feat: per-row start button on runnable flows (0.21.2)

Flows without missing modules get a play button in the list that
opens them directly on the Run tab - one click from the list to
entering inputs and starting a run. Rows with missing modules keep
the install badge as their single actionable path.

Signed-off-by: flemming-it <sf@flemming.it>

CHANGELOG.md

@@ -4,6 +4,15 @@ All notable changes to `chain_studio_flow_editor` recorded here.
 Studio bumps its `pubspec.yaml` git ref to a specific release
 of this package on every editor change.
 
+## 0.21.2 — 2026-07-11
+
+### Added
+
+- **Per-row start button.** Runnable flows (no missing modules) get a
+  play button in the flow list that opens them directly on the Run
+  tab — one click from the list to entering inputs and starting
+  (usertest quick win).
+
 ## 0.21.1 — 2026-07-11
 
 ### Fixed