`_strategy_parameter` docstring `@extref`s `CTBase.Strategies.parameter` with a method signature the inventory does not index

[ocots]

What

The _strategy_parameter docstring in src/helpers/print.jl:335-336 cross-references
CTBase's parameter function by method signature:

[`CTBase.Strategies.parameter(T, default)`](@extref) — the non-throwing counterpart to
[`CTBase.Strategies.parameter(T)`](@extref) requested as [CTBase#518](…)

Neither link resolves. CTBase's auto-generated API reference documents Strategies.parameter
as a single jl:function — one inventory anchor, CTBase.Strategies.parameter, with no
per-method signature. A signature-suffixed @extref only resolves when the target docs split
the docstring per method with a @docs block, which CTBase does not do (and its own #543 fix
did not add per-method anchors — it just rewrote CTBase's prose to drop the suffix).

So this is our bug: the _strategy_parameter docstring replicates exactly the anti-pattern
that CTBase#543 removed from CTBase.

Where it fires

docs/make.jl build → expand_extrefs.jl:93, on the generated api/internals.md
(_strategy_parameter is documented there). 2 of the 6 @extref errors in the
warnonly=[:cross_references, :external_cross_references] backlog — the make.jl comment
(docs/make.jl:266-271) currently attributes them to CTBase#543, which is closed.

The other 4 are CTModels (control-toolbox/CTModels.jl#427).

Fix

Collapse the two suffixed links to the single function anchor, keeping the prose that
distinguishes the two forms:

the two-argument form of [`CTBase.Strategies.parameter`](@extref) — the non-throwing
counterpart to its one-argument form ([CTBase#518](…))

and refresh the docs/make.jl:266-271 comment. Documentation-only; no API or behaviour
change; no version bump.