docs: config engine audit doc fixes (I-01, I-02, I-05)

[DhairyaSethi]

Docs fixes for the Certora config engine review:

• I-01: IAaveV4ConfigEngine and AaveV4Payload.execute() state that every role the executor uses through the engine needs a zero execution delay.
• I-02: the README notes that a dynamic reserve config addition always restates the full config.
• I-05: the sentinel docs name the real per-width EngineFlags values and say that type(uint64).max is forwarded as PUBLIC_ROLE.

The README's delegatecall section now describes the linked libraries instead of the nonexistent *_ENGINE immutables. Stacked on #1367.