feat(simulate): require stable ids in scenarios.yaml, offer to add them

[u9g]

Depends on livekit/protocol#1785 (adds Scenario.id and ScenarioGroup.id). go.mod is pinned to that branch's commit so CI builds; bump to the merged version before merging this.

Why

Today nothing correlates runs of the same scenario over time: the label, instructions, and agent expectations can all be edited, and hashing the content would make every edit a new identity. Dashboards charting a scenario's success rate over time need a stable key.

What

• scenarios.yaml now requires an id on the file and on every scenario. Loading rejects missing or duplicate ids.
• A file missing ids is refused. Interactively the CLI offers to insert generated 8-character ids in place, as the first key of each entry, preserving comments, key order, and indentation (yaml.v3 node edit, no re-marshal). --yes inserts without asking; non-interactive without --yes errors with instructions.
• Scenarios rendered by the CLI (generated runs saved to temp or via the save key, clipboard copy) are given ids so the resulting file runs as-is.
• Ids are sent on ScenarioGroup / Scenario when creating the run. Run-level identity already exists as SimulationRun.id.

Example

id: 3k9fz2ab
name: drive-thru
scenarios:
  - id: q7x1m0dp
    label: order a burger
    instructions: ...

🤖 Generated with Claude Code

[u9g]

Ids now come from protocol's shared guid utility with stable prefixes: SCN_ for scenarios and SCNG_ for the scenario group (livekit/protocol#1785). Dropped the randomBase36 refactor commit since it is no longer needed.