chore(engine): server hygiene batch — workers tests, surname dedup, save pin (T-1063, T-1064)

- workers/pool.rs: 5 new tests; catch_unwind keeps worker threads alive on
  handler panic (in-flight request loss unchanged, pinned by test + #843
  docs); stubs.rs no longer falsely claims the pool is tested
- save/load: execute_save_load pinned .after(Storyteller) so the scheduler
  cannot legally save pre-Input state; exclusive-system exception recorded
  in tick_phases.rs rules
- surname corpus extracted to bin/shared/surname_corpus.rs (both economy
  generators import it; byte-identical output verified on 23.6MB+1.45MB
  TOMLs); all three stamp/watch registries updated
- generator_spike gated behind non-default 'generator-spike' feature
- economy.rs: 11 new D-181 signal-derivation tests on the new
  econ_sim Simulation::from_economy in-memory constructor
- perception exemption comments now state the consumer sort contract;
  unused bytemuck removed; rayon comment corrected; the 22 allow(dead_code)
  documented as serde schema enforcement

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

server/src/workers/stubs.rs

@@ -4,7 +4,10 @@
 //! The actual computation logic is a no-op placeholder — implementations
 //! plug in when the phases that need them arrive (Phase 5+).
 //!
-//! The infrastructure (channels, threads, push/poll) is real and tested.
+//! The infrastructure (channels, threads, push/poll) is real — unit tests
+//! live in `pool.rs` (T-1063). Known limitation (#843): a handler panic
+//! loses the in-flight request (no result is ever delivered, no re-enqueue);
+//! see the crash-behavior notes in `pool.rs`.
 
 use bevy_ecs::prelude::*;