Add desktop GeoTIFF tile server for large-image support

[mattdawkins]

Summary

• Add a geotiff.js + sharp tile server to the Electron backend that reads GeoTIFF/tiled TIFF files and serves PNG tiles via Express routes (/api/tiles/metadata, /api/tiles/zxy/:level/:x/:y)
• Wire the desktop import pipeline (beginMediaImport, loadMetadata) to detect TIFF MIME types and classify datasets as large-image
• Provide getTiles() and getTileURL() in the desktop frontend API so the existing LargeImageAnnotator and GeoJS rendering work on desktop

Details

New file: tileServer.ts — Core tile reading module with LRU-cached GeoTIFF handles (max 10). Supports pyramidal TIFFs (multiple IFDs), non-pyramidal TIFFs (virtual zoom levels with downsampling), and 1/3/4-band raster data with auto-scaling for >8-bit depths.

Import pipeline — Single .tif files and directories containing TIFFs are detected and routed as large-image datasets. Each TIFF file becomes one frame in the dataset, with its absolute path used as the item ID for tile requests.

Build config — geotiff is bundled by webpack (pure JS, avoids ESM/CJS incompatibility with Electron 11). sharp is externalized as a native module.

Test plan

• Import a single .tif file via desktop UI, verify tiled rendering with pan/zoom
• Import a folder of .tif files, verify multi-frame playback
• Draw and save annotations on a tiled TIFF, verify persistence on reload
• Test with untiled (strip) TIFFs, single-band grayscale, and TIFFs without overviews
• Verify existing image-sequence and video imports still work

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