Root cause 1: hydration mismatch — SSR rendered collapsed=true but
client useState initializer read localStorage synchronously, causing
an immediate state change and visual flash. Fix: always initialize
collapsed=true, read localStorage in useEffect so the transition
is smooth (collapsed→expanded animates cleanly).
Root cause 2: three-phase badge rendering (skeleton→letter→favicon)
caused visible state changes. Fix: just show the empty orange badge
until the favicon arrives. No skeleton, no letter fallback. One state
transition: empty→favicon.
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