Npm publishing

[kzhou314]

Plugin-side changes for https://github.com/github/accessibility/issues/10755.
Makes this package installable from npm so the scanner's find action can load it during scan throughnpm install + import.

[Copilot]

Pull request overview

This PR makes the alt-text plugin publishable to npm (with a build output in dist/) so the accessibility scanner can install/import it at runtime, and adds an opt-in model-backed alt-text-quality rule (plus supporting judge infrastructure and extraction context) to detect higher-level alt text quality issues beyond deterministic pattern rules.

Changes:

• Add npm packaging/build setup (tsconfig.build.json, dist exports, prepack build) so the package can be installed/loaded from npm.
• Introduce opt-in alt-text-quality rule backed by GitHub Models (optionally Azure Vision augmentation), including caching and an offline probe harness.
• Expand image extraction + types to capture richer context (intrinsic dimensions, link/button, figcaption, nearby text, page title, section heading) and update tests/fixtures/docs accordingly.

Show a summary per file

File	Description
tsconfig.json	Includes scripts/**/*.ts in the main TS project for typechecking tooling scripts.
tsconfig.build.json	Adds a dedicated build config to emit JS + types into dist/ for npm publishing.
package.json	Switches to a publishable package (@github/...), adds dist exports, and adds build/prepack/probe scripts.
package-lock.json	Locks new dev dependency (tsx) and its transitive deps.
index.ts	Allows rules to be sync or async by awaiting rule.evaluate(ctx).
src/types.ts	Extends ImageRecord with additional context fields and allows async rules.
src/rules/index.ts	Registers the new alt-text-quality rule in the append-only rule registry.
src/rules/alt-text-quality.ts	Implements the model-backed opt-in rule and maps judge verdicts to findings.
src/extract.ts	Enriches extracted image records with context (dimensions, surrounding text, heading/title, link/button, figcaption).
src/utils/fetch-with-retry.ts	Adds retrying fetch helper with timeout + exponential backoff for model/vision calls.
src/utils/load-image-data-url.ts	Adds helper to load images from URL/path/data: and normalize to base64 data: URLs.
src/judges/index.ts	Adds judge factory wiring for copilot vs azure-augmented modes with caching layers.
src/judges/types.ts	Defines shared judge input/output contracts for model-backed judging.
src/judges/prompt.ts	Centralizes system prompt + strict JSON schema for structured verdict output.
src/judges/copilot-judge.ts	Implements GitHub Models judge client using shared prompt/schema and retrying fetch.
src/judges/azure-augmented-judge.ts	Decorator that enriches judge context with Azure Vision pre-analysis (optional).
src/judges/azure-vision-api-client.ts	Implements real Azure Vision Image Analysis 4.0 client.
src/judges/caching.ts	Adds content-hash caches for judge verdicts and Azure vision analyses.
scripts/probe-alt-quality.ts	Adds an offline probe harness for scoring/model agreement on curated fixtures.
schema/config.schema.json	Documents and exposes alt-text-quality as a configurable rule override.
README.md	Documents the new opt-in rule, required tokens/credentials, and workflow env wiring.
.github/workflows/scan-static-sites.yml	Wires job-level env vars for model-backed rule tokens/credentials.
.gitignore	Ignores .env used by the probe harness.
tests/utils/helpers.ts	Updates test helpers/types for richer ImageRecord and sync-vs-async rule evaluation.
tests/unit/vague-alt-text.test.ts	Updates for async-capable rule API (await evaluate).
tests/unit/missing-alt-text.test.ts	Updates for async-capable rule API (await evaluate).
tests/unit/load-image-data-url.test.ts	Adds coverage for data: URL normalization behavior.
tests/unit/judges-caching.test.ts	Adds coverage for caching behavior and error non-caching.
tests/unit/alt-text-quality.test.ts	Adds unit tests for alt-text-quality mapping, skipping, sanitization, and context fields.
tests/extract.test.ts	Adds coverage for page title normalization and nearest preceding heading extraction.
tests/example-site.test.ts	Skips opt-in rules when validating “enabled by default” behavior.
tests/fixtures/alt-quality/cases.json	Adds offline fixture corpus for probe harness and rule evaluation.
tests/fixtures/alt-quality/cases-github.json	Adds GitHub/MDN/W3C-based fixture corpus variants for probing.

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• Files reviewed: 30/33 changed files
• Comments generated: 1
• Review effort level: Low