[WIP] perf: optimize boot time with lazy imports and combined DB queries

[mrosseel]

Summary

• Replace 3 full-table scans (150K+ rows) with 2 targeted JOIN queries for priority catalogs (NGC/IC/M)
• Defer CometCatalog init to background thread (avoids 3-4s network check at startup)
• Defer background catalog loader start until after Event Loop begins
• Remove menu preload flags for UIAlign/UIChart (load on first navigation instead)
• Lazy-import heavy modules: scipy.ndimage, scipy.spatial.transform, sklearn.neighbors, pandas, timezonefinder
• Remove unused startup profiling code

Reduces kernel-relative Event Loop time from ~48s to ~24s on RPi4.

Test plan

• Verify PiFinder boots and reaches Event Loop
• Verify catalog search works (NGC/IC/Messier)
• Verify deferred catalogs (WDS, etc.) load in background
• Verify CometCatalog loads after startup
• Verify UIAlign and UIChart load on first navigation
• Verify plate solving still works
• Run existing test suite

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