Closes #1394.

What

Extracts the four session-scoped UI resets that the disconnect listener in App.tsx performs — the per-call result panels (toolCallState / getPromptState / readResourceState) and the optimistic currentLogLevel — into a colocated resetSessionScopedUiState useCallback. The listener keeps its activeServerId + Connection Info modal-flag bookkeeping inline and calls the helper.

Why now

#1394 was filed as a deferred tripwire during the #1368 review: the note was to extract this helper once App.tsx accrued more per-session state, since four inline setters is below the abstraction threshold. We've opted to do it now anyway so there's a single named seam (resetSessionScopedUiState) to extend as that state grows — the next addition is one line in the helper instead of another setter buried in the listener body.

Notes

• Pure refactor, no behavior change. Same four setters, same reset values, fired at the same point in the disconnect handler.
• latencyMs remains intentionally excluded — it resets via the connectionStatus edge effect, which coordinates with its own connecting-edge ref.
• The helper's deps are [] (the useState setters are stable), so its identity never changes; it's added to the disconnect effect's dep array.
• The existing App.test.tsx disconnect test (asserts all four pieces reset) is unchanged and still passes — it exercises the behavior through the same disconnect event, so it covers the helper transparently.

Verification

npm run validate (1891 tests), npm run test:storybook (322) both pass.

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