Combine train sound selector and large counter

[vbonaci]

Summary

• integrate the selectable train sound work from PR Add selectable train dispatch sounds with localStorage persistence #100
• integrate the large background counter work from PR Add large train dispatch counter #101
• resolve the index.html conflict by preserving theme, sound selection, mute state, and counter bump behavior

Validation

• git diff --check origin/main...HEAD
• served locally at http://127.0.0.1:55020/ and verified HTTP 200 OK

Note: local node is not installed in this workspace, and the Node REPL disallows string code generation, so inline JS parse validation could not be run that way.

[vbonaci]

@mattppal could you review and merge this when you have a chance? The branch combines PR #100 and PR #101, resolves their conflict, and includes a follow-up fix to make the dispatch flow visible.

@LewisJEllis if this should be handled by me directly, can you grant @vbonaci the repo access needed to approve/merge this PR or enable auto-merge? Current permission is read-only, so GitHub blocks approval, normal merge, admin merge, and auto-merge from this account.