Add MessageStore and persona-interaction-tools tests, fix split-pane flake

[selfcontained]

Summary

• Added 14 new MessageStore unit tests covering chronological ordering, 500-message cap, cross-repo messages, undelivered messages, unread counting edge cases, and markRead idempotency
• Added 22 new persona-interaction-tools unit tests covering resolvePersonaList merge logic, buildLaunchPersonaResponseText, and conditional tool registration with all 7 handler behaviors
• Fixed recurring split-pane E2E flake by adding explicit 15s timeouts to waitForAppShell — the default timeout was being consumed by earlier steps, leaving insufficient budget for current-session-name under parallel test SSE interference

Test plan

• pnpm run check passes
• pnpm run test passes (2367 server + 195 web)
• pnpm run test:e2e passes (168 passed, two consecutive green runs)
• Split-pane flake reproduced then confirmed fixed

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