Optimize Paper 26 display hot paths

[TypeThe0ry]

What changed

• decouple display content synchronization from viewer visibility reconciliation
• index sent chunks, shown logical entities, pending viewers, and dropped-item labels
• add bounded visibility restore queues and on-demand dropped-label tasks
• coordinate runnable block displays and workstation sessions on shared schedulers
• cache preference viewer groups and serialize persistent database I/O
• replace LightAPI with on-demand CraftEngine lighting and integrate CraftEngine culling
• apply Typewriter-inspired per-viewer packet tracking for eligible item animations
• add IV_PERF counters and shutdown retained-state auditing
• enable the new-install performance defaults while preserving existing explicit false values

Why

The Paper 26 rewrite still contained global viewer/entity scans, recurring idle tasks, allocation-heavy dropped-label work, and lifecycle state that could survive plugin shutdown. These changes make work scale with sent chunks, nearby candidates, dirty blocks, and pending viewers.

Compatibility and impact

• public InteractionVisualizer API signatures and database schema are unchanged
• Paper 26.1.2 and 26.2 remain the supported targets
• CraftEngine is optional and remains compile-only
• existing performance opt-outs are preserved
• every major optimization retains an independent rollback switch

Validation

• gradlew.bat check shadowJar --no-daemon --rerun-tasks
• Paper 26.1.2 and Paper 26.2 compilation
• unit/property tests
• CraftEngine isolation verification
• Paper-only architecture verification

This draft PR intentionally triggers the short CI A/B smoke campaigns. Formal 12-run ABBA gates should be started only after the smoke workflows are green.

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