FE-1487: Quick simulation runs an ad-hoc scenario when none is selected

[kube]

🌟 What is the purpose of this PR?

The first consumer of the ad-hoc scenario form (FE-778): with no scenario selected, the simulation settings panel offers a "Define initial state" drawer, and the simulation provider compiles the drawer's state through a scenario generated at run time. The generated scenario is never persisted into the net file. Sits above FE-1486 (#9285) in stack #9286.

🔗 Related links

• FE-1487 (internal): this PR
• FE-778 (internal): the umbrella ticket

🔍 What does this change?

react/simulation/context.ts and provider.tsx:

• SimulationContext gains adHocScenario: AdHocScenarioState | null and setAdHocScenario. The setter invalidates the current simulation, the same as every other configuration setter.
• When no named scenario is selected and adHocScenario is set, the provider synthesizes a scenario with synthesizeAdHocScenario and compiles it through the existing compileScenario path. Synthesis errors surface through the existing scenarioCompilationErrors Banner (netParameter errors map to the parameterOverride source, everything else to initialState).
• The panel's parameter inputs stay the single owner of parameter values: the synthesis context's net parameters carry the panel's current values as defaults, and the form receives no parameters section of its own.

simulation-settings.tsx: with "No scenario" selected, a pencil button next to the scenario picker opens the new drawer.

SimulateView/scenarios/ad-hoc-scenario-drawer.tsx: a large Drawer (the prototype's 860px form width) hosting AdHocScenarioForm with optimizable: false. "Clear" resets the ad-hoc state to none; "Done" closes. The form runs its own LSP session, so expressions type-check live against the net.

Pre-Merge Checklist 🚀

🚢 Has this modified a publishable library?

This PR:

• modifies an npm-publishable library and I have added a changeset file(s) (patch).

📜 Does this require a change to the docs?

The changes in this PR:

• add a user-visible surface. The user-guide page ships with the last PR of the stack, once all three consumers exist, so the guide describes the feature once.

🕸️ Does this require a change to the Turbo Graph?

The changes in this PR:

• do not affect the execution graph.

🛡 What tests cover this?

The FE-1485 tests cover synthesis and compilation of everything the drawer can produce. The four extended mock fixtures keep the existing hook, playback, and story tests passing against the widened context.

❓ How to test this?

1. turbo run dev --filter @apps/petrinaut → open a net → Simulate → simulation settings.
2. Leave the scenario picker on "No scenario", press the pencil button, define token rows or counts, close, run the simulation.
3. Pick a named scenario: the drawer button disappears and the named scenario takes over, unchanged.

🐾 Next steps

FE-1488 wires the experiment drawer's no-scenario branch, FE-1489 the optimization drawer with manifest emission (both hold until the experiment-backend PRs #9178/#9179 merge).

🤖 Generated with Claude Code

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