feat(oxlint/linter/lsp): apply bulk suppression baseline - #25093

Summary

Refs #21199 and follows the LSP decisions in #22198.

Teach the oxlint language server to apply oxlint-suppressions.json with the same count-based semantics as the CLI.

Suppressed diagnostics remain visible by default at warn severity. Clients can select hint, info, warn, or error, or hide suppressed diagnostics with suppressedViolationSeverity: "off".

Implementation

• Refactor DiffManager to partition diagnostics into surfaced and suppressed groups without changing existing CLI behavior.
• Load the single suppression baseline from the language-server workspace root, matching the CLI behavior and RFC decision.
• Watch the workspace-root oxlint-suppressions.json so baseline changes rebuild the linter and refresh open documents.
• Log malformed baselines and fail open so diagnostics remain visible. LSP client notification is deferred to draft follow-up feat(oxlint/lsp): report malformed suppression baselines #26543, pending feat(oxlint/lsp): show config errors to LSP client #25486.
• Preserve existing fixes, code actions, related information, and inverted diagnostics for baselined diagnostics that remain visible.

Tests

Add coverage for:

• suppressed diagnostics at every visible severity;
• hiding suppressed diagnostics with off;
• increased and decreased violation counts surfacing at original severity;
• nested suppression files being ignored;
• suppression state reloading after a watched-file change;
• malformed baselines failing open;
• related and inverted diagnostics for visible suppressed violations;
• code actions remaining available on visible suppressed diagnostics.

Extension follow-up

This PR adds native language-server support and publishes suppressedViolationSeverity in the LSP configuration schema. The official oxc-vscode extension does not yet expose or forward this option, so a follow-up extension PR is required for users to customize it through VS Code settings. The default visible-warn behavior works without an extension change.

Verification

• cargo run -q -p website_linter schema-markdown-lsp
• INSTA_UPDATE=always cargo test -q -p website_linter test_schema_markdown_lsp (1 passed)
• git diff upstream/main...HEAD --check

Full lint, build, typecheck, and test coverage is left to CI.

AI assistance

Codex was used to investigate, implement, test, and draft this change.