feat(traits): implement ControlDependence on Model; migrate is_control_free/has_control to CTBase

[ocots]

Summary

Implements the new CTBase.Traits.ControlDependence trait (added in CTBase 0.26) on Model, and migrates the is_control_free / has_control predicates from CTModels-local definitions to the generic CTBase functions. This is PR2 of the ecosystem-wide traits cleanup (CTBase → CTModels → CTFlows).

What changed

1. Model implements the control-dependence contract (src/Models/model.jl):

   • has_control_dependence_trait(::Model) = true
   • control_dependence(ocp::Model) reads the control model type: EmptyControlModel → ControlFree, any other → WithControl
   • This mirrors the existing variable-dependence design verbatim (read from the field type, not the dimension)

2. is_control_free / has_control migrated to CTBase.Traits (src/Models/Models.jl):

   • Removed the bespoke runtime definitions (control_dimension(ocp) == 0)
   • Now imported from CTBase.Traits and re-exported, so CTModels.Models.is_control_free / has_control keep working unchanged
   • Bonus: is_control_free is now type-stable (derived from the control model type)

3. Dependencies: CTBase compat 0.25 → 0.26; version 0.13.3-beta → 0.14.0-beta

4. Tests (test/suite/models/test_variable_control_checks.jl): extended the control-free / with-control cases with trait-path assertions (control_dependence, has_control_dependence_trait, has_control)

5. Docs: added a Control dependence subsection to the model Types and traits guide

Why this matters

Control presence is a genuine dispatch axis. PR3 (CTFlows) will dispatch Flow(ocp) on control_dependence(ocp) to route control-free vs with-control problems, closing a latent bug where a with-control OCP would silently mis-build a Hamiltonian. This PR makes the trait available on Model (its proper home, avoiding type piracy in CTFlows).

Verification

• Tests: models/components/display suites 313/313 passing (including extended control-checks)
• Docs build: succeeds (exit 0). The @ref warnings for is_control_free/has_control are identical to the pre-existing is_autonomous warning on the same page (imported CTBase predicates, no InterLinks) — consistent, tolerated via warnonly
• Smoke test: control_dependence dispatches on Model; is_control_free/has_control confirmed === CTBase.Traits.* (re-export preserved)

Compatibility

No breaking changes — predicate names and behaviour preserved via re-export. Requires CTBase ≥ 0.26.0-beta. See BREAKING.md.

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