Show execution-time badges for subgraphs and their internal nodes

### What problem are you experiencing?

Execution-time/runtime badges are useful for finding slow nodes, but subgraphs currently hide this information. The subgraph node does not show how long the subgraph took to execute, and the nodes inside the subgraph do not show their individual execution times when the subgraph is opened.

This makes performance debugging much harder after organizing a large workflow into subgraphs.

### When does this problem occur?

Whenever a workflow containing subgraphs is executed and I want to identify which subgraph or internal node is responsible for most of the runtime.

Expected behavior after execution:

- Each executed node inside an opened subgraph shows its normal individual runtime badge.
- The subgraph node shows one aggregate runtime badge for the complete subgraph.
- For nested subgraphs, the same behavior works recursively.
- Badges represent the most recent execution and survive switching workflow tabs consistently with regular node runtime badges.

The aggregate value should preferably be the subgraph's wall-clock duration (first executed child start to last executed child completion), rather than a simple sum of child durations, so parallel branches are not double-counted.

### How often do you encounter this problem?

Multiple times per day

### How much does this problem affect your workflow?

Causes moderate inconvenience

### Current workarounds

Open execution logs or temporarily move nodes out of the subgraph. Both approaches remove the at-a-glance performance information that runtime badges provide on regular nodes.

### Ideas for solutions (Optional)

Use locator-scoped execution timing for internal nodes, then aggregate the executed descendant interval for the subgraph host node. The existing runtime-badge visibility setting should control both regular and subgraph timing badges.

### Additional context

Checked against the currently shipped frontend `1.45.21`, current standalone release `1.48.3`, and frontend `main`. I could not find existing subgraph runtime-badge support or a matching issue/PR.

Start by tracing the existing runtime-badge visibility and execution-timing behavior in the frontend, then inspect how opened, nested subgraphs expose their executed nodes. Verify the change with workflows containing sequential, parallel, and nested subgraphs: internal nodes should show individual recent runtimes, host nodes aggregate the subgraph interval, and badges should persist across workflow tabs.

Written by the indexing model from the issue text.