[M1-ECS-02] Component registry + trait-based IDs

[offdev]

Implements M1-ECS-02 from roadmap/M1-heartbeat.md (exactly the Scope bullets, nothing else).

What landed

• ComponentTypeId — stable per-world component type ids: 32-bit, dense in registration order from 1, 0 reserved (kInvalidComponentTypeId). Assignment is pure integer bookkeeping (ARCH-010): same registration order → bit-identical ids across worlds/runs/builds. Per-world ids (cross-world caveat, like Entity). operator< orders by registration order for M1-ECS-03/05.
• LAIGE_COMPONENT(Type) — compile-time trait mark (data-only; replication/inspector traits land in M4). Built-in and user-defined components register through the same path — a user struct is legal (S-8 data-carrier case, PRD Appendix B shape).
• World::registerComponent() — records sizeof(T)/alignof(T) for the M1-ECS-03 SoA layout. Duplicate registration is an error (InvalidArgument + rate-limited warn ecs/component_duplicate); engine-level budget kMaxComponentTypes = 256 (BudgetExhausted); setup-phase O(n), no allocation; moved-from world has no registry. Type identity without RTTI/unordered containers (per-type inline-static marker address; NFR-8.10, PERF-006). static_assert guards: LAIGE_COMPONENT mark + trivially-copyable (actionable compile errors).
• componentCount() / componentInfo(id) accessors; registry moves with World; clear() leaves it untouched.

Files

• New: src/laige-sim/include/laige/sim/component.h, tests/laige-sim/component_registry_tests.cpp, docs/api/component_registry.md
• Modified: entity.h/.cpp (World registry), tests/laige-sim/CMakeLists.txt (component_registry CTest entry), docs cross-refs (docs/README.md, docs/api/entity.md, src/laige-sim/README.md), roadmap (box, board 2/25, change log), laige-api.json (regenerated: 421 symbols)

Verification (AGENTS §5)

• ctest -R component_registry green — 12 cases (duplicate error + unchanged registry, id stability across two worlds with the same registration order, order-determines-ids, 256-type budget boundary, size/alignment incl. 8-byte alignment, componentInfo validation, move/clear, warn-once rate-limit summary via memory sink)
• Full ctest 35/35 on canonical g++ Debug tree (zero warnings, -Werror), ASan+UBSan tree 35/35 (leak-free), Clang tree 35/35; shared-library tree builds clean
• api-real-tree green after manifest regeneration; tools/laige-include-lint OK (1/10 deps)
• No hot-path changes (registration is a setup-phase operation); zero-allocation property holds by construction (no new heap on any operation)

No ENGINE-RULE-EXCEPTION added.