docs: clarify priority ordering behavior

[asllanmaciel]

Clarifies how component priorities should be used when customizing the environment.

The documentation now explains that:

• higher priorities are attempted first;
• block start parsers, inline parsers, and renderers should not rely on registration order when priorities tie;
• explicit, different priorities should be used whenever execution order matters;
• event listeners retain their documented same-priority registration order;
• the rendering guide explicitly calls out the renderer tie case that caused the confusion in addRenderer and addExtension inconsistency #1023.

This is documentation-only and does not change runtime behavior.

Verification:

• git diff --check — pass
• documentation consistency checks for the #priority links, tie guidance, and event-listener exception — pass
• branch is 1 commit ahead / 0 behind 2.10

AI assistance was used to help review the relevant priority semantics and prepare the documentation patch; the final diff and source behavior were reviewed directly.

Refs #1023.

[colinodell]

Thank you for the contribution! Overall, these changes look great and will be very helpful to users.

I'm adding a few minor tweaks, but nothing that significantly changes what you've added.