[Compatibility] Replace exact Codex-version gating with behavior-based capability probes

[pate0304]

Outcome

Keep Codesemble useful across evolving Codex releases without inventing unsupported settings.

Acceptance criteria

• The agents-v1 adapter is selected from documented behavior and strict disposable validation rather than an exact 0.145 minor lock.
• Custom-agent required fields, config precedence, project trust, nested instructions, permission profiles, model catalog parsing, and fresh-session activation are tested.
• Experimental model discovery fails closed to inheritance.
• Agent reasoning-effort routing is verified against actual child context.
• Unsupported runtimes fall back to manual or unchanged configuration without writes.