feat: Replace number with bigInt for ids

[afonsobspinto]

Closes https://metacell.atlassian.net/browse/NA-781

Done exclusively by codex GPT-5.5:

Summary

• Migrated spatial skeleton IDs to bigint across the public skeleton API, caches, navigation, selection, hover, command history, edit state, CATMAID integration, and UI state.
• Added shared ID helpers in src/util/bigint.ts for parsing positive uint64 IDs, bigint-safe sorting, and decimal string formatting.
  CATMAID now keeps IDs as bigint internally, serializes request/form/JSON boundary values with .toString(), and rejects unsafe numeric IDs instead of rounding them.
• Updated command payload validation so legacy safe numeric inputs can enter at payload boundaries, but command state stores bigint IDs.
• Updated tests to use bigint IDs, including large IDs above Number.MAX_SAFE_INTEGER.

Rendering / Shader Changes

• Spatial skeleton segment vertex attributes changed from DataType.UINT32 to DataType.UINT64.
• Segment and node metadata arrays now use BigUint64Array, including nodeIds, pickNodeIds, pickSegmentIds, and pickEdgeSegmentIds.
• Shader segment handling now uses the existing uint64 path:
  • segment attribute/varying is represented as highp uvec2
  • shader converts to uint64_t
  • color/alpha lookup uses the uint64 segment appearance path instead of truncating through highp uint
• Chunk CPU-side pick resolution preserves 64-bit IDs by copying packed segment attribute bytes into aligned BigUint64Array.
• Overlay geometry now deduplicates/links nodes with Map<bigint, number> and emits bigint pick metadata, so selected-node marking and parent-edge picking preserve full IDs.