Report found blocks only after accepted shares

[0xjc65eth]

Summary

• keep updating best/session difficulty as soon as a nonce is found
• mark block candidates as pending only after the share is successfully submitted
• increment blockFound and show the block banner only when the pool accepts a pending block candidate
• clear pending block candidates when the pool rejects the matching pending share path

Why

A nonce can meet network difficulty but still fail to become a valid pool-accepted block candidate if it is never submitted or is rejected. The dashboard should not report a found block until the pool has accepted the submitted share.

Fixes #1552.

Testing

• git diff --check

Full firmware build was not run locally because idf.py is not installed in this shell and the Docker daemon is not running.

[0xjc65eth]

Closing this for now to reduce maintainer review load, per feedback from @mutatrum. I am keeping #1705 open as the single focused PR because it is small, UI-only, and already has an ack. Happy to revisit this later only if maintainers ask for it. Thanks for the feedback and for maintaining the project.