Implement the AutoCAD compatible HATCHTOBACK (HB) command and enhance the interactive DRAWORDER command pipeline with comprehensive verb selection and viewport entity picking.
Key implementations and architectural details:
1. HATCHTOBACK command execution
* Isolates entities belonging to the active layout block record or global space.
* Filters out entities residing on locked layers using an efficient hash set lookup.
* Records targeted delta undo operations on SortEntitiesTable objects (~100 bytes) rather than snapshotting full document structures.
* Performs granular draw depth cache invalidation via Scene::invalidate_draw_depth, preserving existing geometry tessellations and spatial indices.
* Emits localized user notifications when no qualifying hatch entities are found.
2. Interactive DrawOrderCommand state machine
* Supports preselected entities as well as interactive on demand selection gathering.
* Implements subverb selection supporting single character shortcuts (A for Above, U for Under, F for Front, B for Back) and case insensitive keyword parsing.
* Enables interactive reference object picking directly in the viewport via needs_entity_pick and on_entity_pick callbacks.
* Supports hexadecimal handle specification directly from the command line interface.
3. Ecosystem and system integration
* Bumps DEFAULT_ALIASES_VERSION from 2 to 3 to register the HB alias while preserving existing user overrides.
* Integrates HATCHTOBACK and HB into dynamic autocomplete registries.
* Adds localized message strings across all 20 Fluent translation catalogs.
* Corrects hatch boundary serialization flags to ensure outermost boundary rings consistently carry the external attribute.
Persist camera, render state, and solid fallback geometry across saves. Generate previews from a clean live viewport and refresh recent-file thumbnails immediately.
Temporary fence pieces used a sentinel handle, so the source spline was included as its own cutting boundary and kernel intersection recursed indefinitely.
Refs #830
