Refactor app validation errors: result-based parsing, structured error data

[ryancbahan]

What

Refactor app validation error handling from throw/catch with styled OutputMessage to result-based parsing with a plain ConfigurationError data interface.

Why

Prep for app config validate --json (see #7066, #7090, #7106). The original stack added structured error data alongside rendered messages, creating dual-track serialization in the loader. This PR takes the opposite approach: make errors pure data, let callers render. This gives callers more flexibility and removes the job of rendering/formatting from the data flow.

How

• ConfigurationError is now a plain interface ({file, message, path?, code?}), not a class extending AbortError
• parseConfigurationObject, parseConfigurationObjectAgainstSpecification, parseConfigurationFile return {data} | {errors: ConfigurationError[]} instead of throwing
• AppErrors stores ConfigurationError[] with addError, addErrors, getErrors(file?), isEmpty
• formatConfigurationError is the single plain-text formatting function
• Styled output (outputContent/outputToken) applied only at display boundaries: app-context.ts (AbortError), validate.ts (renderError), loader.ts (reloadApp)
• parseStructuredErrors in error-parsing.ts converts Zod issues to ParsedIssue[] with union-variant scoring

No user-facing behavior changes. CLI output preserves styling. Multi-error-per-file now preserved (previously silently overwritten by dictionary key).

[github-actions]

We detected some changes at packages/*/src and there are no updates in the .changeset.
If the changes are user-facing, run pnpm changeset add to track your changes and include them in the next release CHANGELOG.

Caution

DO NOT create changesets for features which you do not wish to be included in the public changelog of the next CLI release.

[ryancbahan]

• Add errors to TomlFile and Project for TOML parse failure tracking #7130
• Add structured {valid, issues} JSON contract for app config validate #7128
• Refactor app validation errors: result-based parsing, structured error data #7126 👈 (View in Graphite)
• main

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