4870 - Add Edit button to open Subflow from Execution Island

[petrapaz]

fixes #4870

Description:

• Adds an Edit button to the subflow task detail panel in the Execution Island.
• Clicking it navigates to the subflow's workflow editor, closes the execution panel, and shows a "Currently inside a subflow" banner with a "Return to parent flow" button.
• On return, the parent's execution panel is restored if it was open.
• Nested subflow navigation is supported via a parentChain URL param stack.
• Opening subflow executions is out of scope and tracked separately.

Video example:

Screencast.from.2026-05-28.16-11-11.webm

Possible enhancements for nested subflow executions:

Multi-level execution snapshot - currently only the top-level parent's execution is snapshotted. A map keyed by projectWorkflowId (mirroring the parentChain URL stack) would restore execution panels at every level of nesting, not just the root.
Intermediate panel restore - returning from subflow2 → subflow1 currently doesn't restore subflow1's execution panel (only root restore is implemented). Would require the multi-level snapshot above.
Execution panel per workflow - instead of a single global workflowTestExecution slot in Zustand, key executions by projectWorkflowId so each workflow remembers its own last execution independently of navigation.

[sonarqubecloud]

Quality Gate failed for 'client'

Failed conditions
0.0% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud