feat(core): extract shared KbqCheckable primitive (#DS-3498)

[NikGurev]

Summary

Checkbox and toggle each reimplemented the same checked/disabled/indeterminate/
tabIndex state, click-to-toggle algorithm, ARIA-checked computation, FocusMonitor
wiring, and ControlValueAccessor - toggle even imported checkbox's internals
(TransitionCheckState, click-action token) to avoid re-declaring them.

• Add KbqCheckable (@koobiq/components/core), a hostDirective centralizing all
  of the above, including its own ControlValueAccessor registration so any
  future control built on it gets form support for free.
• Wire KbqCheckbox and KbqToggleComponent onto it via hostDirectives with zero
  public API changes; toggle now depends on the generic KBQ_CHECKABLE_CLICK_ACTION
  token (falling back to KBQ_CHECKBOX_CLICK_ACTION for backwards compatibility)
  instead of reaching into the checkbox package.
• Add an example-block-checkbox doc example showing a custom checkbox-like
  "card" control built directly on the primitive.

[github-actions]

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[Copilot]

Pull request overview

This PR extracts the duplicated checkbox/toggle state machine into a shared KbqCheckable host directive in @koobiq/components/core. KbqCheckable centralizes the checked/disabled/indeterminate/tabIndex signals, the click-to-toggle algorithm, ARIA-checked computation, FocusMonitor wiring, and ControlValueAccessor registration. KbqCheckbox and KbqToggleComponent are rewired onto it via hostDirectives, TransitionCheckState and the click-action token/type are promoted to core (with deprecated aliases kept in the checkbox package for compatibility), and a new "block checkbox" doc example demonstrates building a custom control on the primitive.

Changes:

• Add KbqCheckable primitive plus KbqCheckableClickAction, KBQ_CHECKABLE_CLICK_ACTION, KbqCheckableClickResult, and moved TransitionCheckState to core.
• Rewire KbqCheckbox/KbqToggleComponent onto KbqCheckable, delegating state, CVA, focus, and click handling; keep public APIs stable via deprecated aliases.
• Add a block-checkbox docs example and its registration/documentation.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packages/components/core/common-behaviors/checkable.ts	New shared KbqCheckable directive with state, CVA, focus, and click logic.
packages/components/core/common-behaviors/index.ts	Re-exports the new checkable module.
packages/components/checkbox/checkbox.ts	Delegates state/CVA/focus/click to KbqCheckable; deprecates old CVA token and re-exports TransitionCheckState.
packages/components/checkbox/checkbox-config.ts	Aliases KbqCheckboxClickAction to the core type.
packages/components/toggle/toggle.component.ts	Rewires toggle onto KbqCheckable; adds KbqToggleClickAction; uses the checkable click-action token with a checkbox fallback provider.
packages/docs-examples/components/checkbox/block-checkbox/*	New example component/styles built on KbqCheckable.
packages/docs-examples/components/checkbox/index.ts	Registers BlockCheckboxExample.
packages/components-dev/checkbox/module.ts	Adds the example to the dev app.
packages/components/checkbox/examples.checkbox.{en,ru}.md	Documents the block checkbox example.
tools/public_api_guard/components/{core,checkbox,toggle}.api.md	API snapshot updates reflecting the moved/added symbols.

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