Add comprehensive state constraint example with Bryson-Denham problem

[ocots]

This PR adds a comprehensive state constraint example to the documentation, starting from the extraction of a first-order constraint example and extending it with a detailed second-order constraint (Bryson-Denham problem) treatment.

Initial commit (76e5a30): Extracted the state constraint example from example-double-integrator-energy.md into a separate autonomous file example-state-constraint.md. This refactoring improves documentation organization by:

• Creating a dedicated example for state-constrained optimal control
• Adding cross-references between the energy minimization and state constraint examples
• Updating the Basic Examples menu in make.jl

Main additions:

1. Second-order state constraint (Bryson-Denham problem): Added a complete treatment of the position constraint q(t) ≤ a with boundary conditions x(0) = (0,1), x(1) = (0,-1), including:

   • Corrected solution structure based on Bryson & Ho (1975): touch point regime for 1/6 ≤ a ≤ 1/4, boundary arc regime for a < 1/6
   • Theoretical references: Bryson et al. (1963), Jacobson et al. (1971), Bryson & Ho (1975)

2. Direct method: Implemented parametric OCP via make_ocp(a) function to avoid code duplication, solving both cases (a=0.2 touch point, a=0.1 boundary arc) in a single workflow

3. Indirect methods:

   • Touch point case (a=0.2): 2-arc structure with costate jump at contact time
   • Boundary arc case (a=0.1): 3-arc structure with boundary arc flow and costate jumps at entry/exit
   • Both include shooting functions, initial guess extraction from direct solutions, and Hamiltonian-based adjoint chain explanations

4. Code quality improvements:

   • Harmonized entry/exit time extraction using findall pattern
   • Added return nothing to shooting functions
   • Improved plot superposition and transitions

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Breakage test results
Date: 2026-04-14 19:40:27

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