Model random values with scenario-supplied randomness #65

Context

Bastion on athena-sim now stops at value randomInteger at tick 0 (after athena#57 merged). Parent: #45.

Problem

Random Integer, Random Real, Random Value In Array, Random Number-family values and Randomized Array are nondeterministic in the client. The simulator must stay deterministic and must not guess (see docs/findings.md).

Requirements

• Scenario input supplies randomness: an optional scenario field (seed or explicit sequence of draws) that the simulator consumes in evaluation order. Choose the smallest shape; document it in docs/scenario-format.md and docs/scenario.schema.json.
• With a supplied source, random values evaluate deterministically from it; ranges, inclusive bounds and array selection follow the workshop-rs catalog description. The mapping from draws to values is recorded modeled-not-measured (no client capture of the distribution).
• Without a supplied source, the run ends missing_input naming the random input (not not_modeled, not a hidden default seed).
• The trace records that a random draw happened (rule, value) so the viewer can show it.
• Run Bastion with a scenario that supplies randomness and record the next stop in the PR body.

Acceptance criteria

• Tests: same seed gives identical traces; different seed can differ; missing source gives missing_input; bounds (min==max, min>max handling per catalog), Random Value In Array on empty array, Randomized Array keeps the elements.
• Docs updated: simulator-interface, scenario-format, findings.
• fmt, clippy -D warnings, cargo test, wasm32 check pass.