fix(ui): ignore stale sequence timeouts

[guyua9]

A delayed double-key timeout can arrive after the REPL has started executing a query. The old handler only checked the sequence number and could reset StateExecuting to StateInput, hiding the running query and changing cancellation/input behavior.

This change:

• limits seqTimeoutMsg state transitions to pending clear/quit states;
• invalidates pending sequence ticks on completion, abort, and interrupt paths;
• clears the pending status message when a sequence is abandoned;
• adds model-level regression coverage for stale timeout and status cleanup.

Validation:

• GOPROXY=direct go test ./...
• GOPROXY=direct go vet ./...
• git diff --check