orb validate rejects parameter expressions in fields with regex value-pattern validation

## Summary

`circleci orb validate` (CLI 0.1.34950) rejects valid orb authoring patterns that put a `<< parameters.X >>` placeholder into a string field whose schema has a `pattern:` (regex) value check. The validator runs the regex against the literal placeholder string instead of deferring it until after parameter substitution. Integer parameters work fine because their schema skips the pattern step.

## Reproducer

[orb-tools/pack failure on cypress-io/circleci-orb#577](https://app.circleci.com/pipelines/gh/cypress-io/circleci-orb/2179/workflows/ba990d9c-bf5e-4b70-a3bd-0bc5e355881d) — minimal repro is a `run` step with both keys threaded from parameters:

```yaml
parameters:
max-auto-reruns:
type: integer
default: 0
auto-rerun-delay:
type: string
default: "0s"
steps:
- run:
command: << parameters.cypress-command >>
max_auto_reruns: << parameters.max-auto-reruns >> # passes
auto_rerun_delay: << parameters.auto-rerun-delay >> # FAILS
```

## Failure

```
[#/commands/run-tests/steps/1/run/auto_rerun_delay]
string [<< parameters.auto-rerun-delay >>]
does not match pattern ^((10|[1-9])m|([1-9][0-9]*)s)$
```

The cascading errors above this line ("extraneous key [run] is not permitted", "expected type: String, found: Mapping") are the validator's confused fallback after the run-step subschema fails to match — the root cause is the single `auto_rerun_delay` regex check.

## Expected behavior

Either:
- Defer regex/pattern checks until after parameter substitution, OR
- Recognize `<< parameters.X >>` (and other [parameter expression syntax](https://circleci.com/docs/reusing-config/#using-the-parameters-declaration)) as a valid placeholder for any string field with a `pattern:` constraint.

The existing integer handling (passes `<< parameters.max-auto-reruns >>` cleanly when the field is typed `integer`) is the right precedent.

## Workaround

Drop the parameter and hardcode the value in the orb, or omit it and rely on the runtime default. This is what cypress-io/circleci-orb#577 ended up doing.

## Affects

- CircleCI CLI 0.1.34950 (latest at filing)
- Any orb author who wants to expose a parameter for a string field that has `pattern:` validation in the orb schema (`auto_rerun_delay`, possibly other recently-added timing/duration fields).

## Environment

- macOS 15.4 (Darwin 25.4.0)
- `circleci version` → `0.1.34950+8ff907b (homebrew)`

Start at the `circleci orb validate` entry point and reproduce the YAML example with a string parameter in the `auto_rerun_delay` pattern-validated field. Trace the pattern validation and parameter-expression handling; done means valid placeholders are accepted while literal values that fail the regex remain rejected.

Written by the indexing model from the issue text.