Add a configurable skill catalog token budget (#38978)

## What changed

- Add `[skills].max_context_tokens` to override the token budget used to render the available-skills catalog.
- Require a positive value and cap configured budgets at 10,000 tokens.
- Preserve the existing default of 2% of the model context window when the option is unset.

## Testing

- Cover configuration parsing, override behavior, the 10,000-token cap, and catalog rendering within the configured budget.

GitOrigin-RevId: f29ddcb57fc2d800c0006d03e1c33cbe3ab6272d

codex-rs/cli/src/main.rs

@@ -2127,6 +2127,7 @@ async fn run_debug_prompt_input_command(
     codex_skills_extension::install(&mut extensions, |config: &Config| {
         codex_skills_extension::SkillsExtensionConfig {
             include_instructions: config.include_skill_instructions,
+            max_context_tokens: config.skill_max_context_tokens,
             bundled_skills_enabled: config.bundled_skills_enabled(),
             orchestrator_skills_enabled: config.orchestrator_skills_enabled,
             shadow_selection_enabled: config