docs: Phase 2 — the engine is its own Rust→WASM crate

[Kinflou]

The simulation moved out of the playground TypeScript into ComlineProject/simulator — a Rust crate → WASM, built on comline-runtime directly and structured as a discrete-event simulation. This revises the Phase 2 spec to match 10 PRs of implementation.

• New Architecture section — why a separate crate (real runtime contract, no vendored port / drift guard, sync DES engine, Shape-JSON boundary instead of linking comline-core), the module layout, the script cargo feature + wasm-size note.
• §2f rewritten — a sandboxed Rhai script, not a Worker-sandboxed JS snippet. Safe by construction (no I/O), resource-limited (operations / call-level / size caps), state persists between calls.
• 2h subsumed — the Rust engine already runs the real comline-runtime contract via GenericDispatch, so "route A vs route B" and the drift guard no longer exist. The esbuild-wasm risk is moot.
• 2a–2f marked done (PRs docs: CC-BY-4.0 + record the licensing decision #1–#10 on the simulator repo); 2g, the playground rewire, and 2i remain.
• §2c / 2d / 2e updated to the shipped behaviour (timeout/dead, the single stepped clock, deterministic-by-construction replay).
• Open questions / Risks pruned of the esbuild-wasm and Worker-CSP items; added the scripting-wasm-size and playground-rewire-scope questions.

mkdocs build --strict clean.