fix: Update max privval size

[Eric-Warehime]

Updates the max privval message size to mirror changes made upstream. This fixes the possibility of a large vote-extension enable precommit with mldsa validator exceeding the older default.

[greptile-apps]

Greptile Summary

This PR raises the remote-signer message limit to support larger vote-extension precommits. The main change is:

• Derive the framing cap from the maximum vote-extension and signature sizes instead of using a fixed 10 KiB limit.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
internal/manager/manager.go	Replaces the fixed remote-signer framing limit with a size derived from supported vote extensions and signatures.

_{Reviews (1): Last reviewed commit: "Update max privval size" | Re-trigger Greptile}