refactor(lint-cli): lint.rs output-matrix ResultSink redesign

[dean0x]

Summary

Refactor the output-path architecture in lint.rs to consolidate the ResultSink trait — the pattern that makes --quiet structurally unbypassable and replaces 13 ad-hoc stdin-label sites.

This work unblocks five previously fixed defects (complexity-01, complexity-02, and three earlier wave fixes) and eliminates the prose contracts that complexity-12 tried to document.

Deferred Issues

From review [wave-v0.4.0-wave1/2026-08-19_1216]:

Finding	File:Line	Reason
complexity-04	crates/mds-cli/src/lint.rs	B1 ResultSink refactor — rewrites every output path at a release gate.
complexity-12	crates/mds-cli/src/lint.rs:18	Prose PF-004 contract obsoleted by complexity-04.
performance-02	crates/mds-cli/src/lint.rs:1309	Touching sort key + display path together risks the just-declared ordering contract.
architecture-03	crates/mds-cli/src/lint.rs:770	Stdin-label funnel touches 5 files across every CLI output path.

Acceptance Criteria

• ResultSink trait introduced as the output abstraction
• All output paths (JSON, quiet, default) route through ResultSink
• --quiet mode is unbypassable at the type level
• Stdin labeling consolidated to a single codepath
• All four defects resolved

Related

• PR v0.4.0 Wave 1: breaking changes, live-bug fixes, and release-safety gates #308 (wave/v0.4.0-wave1)
• Implements solution to: complexity-01, complexity-02

For v0.5.0