Integrate style rules from ALLinter into YAML checker

[nonprofittechy]

1. Makes it easier to run from command line
2. Lets us run style checks from ci/cd for appropriate interviews; also simplifies integration with the Weaver

Copied over all of the pure style rules, but also there was some mismatch in accessibility checks which were duplicated between the two repos.

Style checks are only run when explicitly requested with the --style flag. Using --style-llm also runs LLM-powered checks for readability that deterministic rules aren't flexible enough for. When using --style-llm, developer can either use environment variables for OPENAI_BASE_URL, _MODEL, and _API_KEY, or pass as flags.

This is designed to be an importable feature for the existing Dashboard linter, rather than a duplicate copy of those rules.

[Copilot]

Pull request overview

This PR integrates Assembly Line interview “style” lint rules into dayamlchecker, making them runnable from the CLI and enabling CI/CD style checks (including optional LLM-backed rules), while also expanding accessibility parity coverage.

Changes:

• Add opt-in deterministic style linting plus optional LLM-backed style findings (CLI flags + Python helper).
• Add interview-level parity checks (missing question id, multiple mandatory blocks, missing common metadata fields).
• Expand accessibility lint rules/messages and add parity tests; package YAML data files needed for style rules.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/test_yaml_structure.py	Adds parity tests for new interview-level + accessibility rules; updates “valid question” fixture.
tests/test_style.py	New test suite covering opt-in style checks, severities, LLM configuration behavior, and CLI integration.
src/dayamlchecker/yaml_structure.py	Wires style/interview-level linting into the main parser flow; adds CLI flags and a style-only helper.
src/dayamlchecker/style.py	New style lint engine (deterministic + optional LLM rules) and prompt/data loading.
src/dayamlchecker/messages.py	Adds new FindingClass.STYLE, new message IDs, and message definitions for accessibility/style/interview-level findings.
src/dayamlchecker/accessibility.py	Adds multiple new accessibility checks (labels, choices, validation guidance, HTML rules, etc.).
src/dayamlchecker/data/plain_language_replacements.yml	Adds plain-language replacement dictionary used by style linting.
src/dayamlchecker/data/interview_linter_prompts.yml	Adds LLM prompt templates/rules for style linting.
src/dayamlchecker/init.py	Exposes a small public API surface for Python consumers (including style helper).
README.md	Documents style linting usage via CLI and Python helper.
pyproject.toml	Ensures new YAML data files are included in the package distribution.

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[nonprofittechy]

This is mostly a straight lift of the existing linter, but it's large enough I won't expect a code review. Any suggestions welcome; this is totally opt-in at the moment, and has been validated manually against a sample of ~ 70 of our repos.