perf: speed up sidebar navigation

[Talljack]

Summary

• remove the blocking i18n loading screen and defer non-critical app bootstrap work
• dedupe repeated IndexedDB/localStorage hydrations for content, favorites, wordbooks, and TTS settings
• cache module session counts and reuse dashboard analytics data instead of rescanning the same tables

Verification

• pnpm build
• local production-mode browser check on 2026-06-04: sidebar navigation Dashboard -> Listen -> Read -> Write -> Dashboard completed in roughly 47-90ms per click across 3 rounds
• confirmed the blocking "Loading your language settings" overlay no longer appears during navigation

[vercel]

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Project	Deployment	Actions	Updated (UTC)
echo-type	Building	Preview, Comment	Jun 4, 2026 1:02am