[snkmcb]

Summary

• Adds public NumberDragDispatcher and number_drag_target (number_drag.hpp) for horizontal pointer scrubbing over every NumberInput and VectorInput component. No new parts, roles or document vocabulary.
• A primary press on an input's label, field or padding captures the pointer and focuses the input. After a 3-unit horizontal threshold, moves and the release request whole steps of 4 units from the press (truncated toward zero) through the input's own command, only when the count changes. Both distances are configurable.
• started tells the host to record the origin value. Escape/Cancel while scrubbing requests 0 steps (canceled). PointerCancel keeps the last value. Other key, text and logical input ends capture unconsumed. Replacement keeps a compatible capture by author ID. Step parts are not targets.
• Inspector: Scale and Position X/Y/Z scrub from their parsed drafts. An invalid draft rejects with the existing feedback. The captured control shows its active background, and Windows shows the horizontal resize cursor over scrubbable inputs. The hint now reads "Enter applies, Esc reverts, Up/Down or drag step."
• Docs: new input architecture section, NumberInput/VectorInput/Inspector guide sections, support matrix, testing table, changelog.

Verification

• New owner test number_drag: targets, click vs. threshold, truncated steps, cancellation, replacement, rejection.
• inspector_hierarchy window-free smoke: new scrub_smoke. The injected native smoke drags the X label under OS capture.
• Debug: all 98 non-native tests pass.
• Release: number_drag, inspector_hierarchy and inspector_hierarchy_native pass (native 13 s).
• scripts/check-docs.ps1 passes. Formatted with clang-format 23.1.1.

Note: in Debug, inspector_hierarchy_native exceeds its 60 s CTest timeout (it passes standalone in 155 s). This change adds only three injected messages, so the slow Debug run is very likely pre-existing. I did not re-measure it on main.

Not included

Modifier-scaled or vertical scrubbing, scrub history transactions in the Inspector (each change is a separate command, like the Display color drag), pointer caret placement, native accessibility.

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