Support per-file lint configuration overrides - #38

Summary

Addresses #35. Originally stacked on #37; that PR is now merged. This PR targets master and includes the latest base changes.

• Share effective lint configuration between Volt.JS.Check and mix volt.lint.
• Add root-relative, ordered overrides for rules, environments and globals. Later matches replace individual entries; environment maps can disable inherited environments and globals can be set to :off.
• Apply global environments/globals in mix volt.lint as well. Preserve CLI plugin precedence and run-wide custom rules.
• Batch type-aware checks by effective TypeScript rules, matching overrides against original Vue/Svelte paths while retaining all extracted source overrides and restoring diagnostic paths.
• Document matching/merge semantics and update the Unreleased changelog. File discovery and formatting configuration remain unchanged.

Validation

• Reproduced the ignored-override failure before implementation.
• mix ci: 706 passed, 5 skipped, 39 excluded. Includes formatting, native JS/type-aware checks, Credo, architecture/dead-code checks and Dialyzer.
• Regression coverage includes generated filename exemptions, scoped no-null, both Mix commands, disabling inherited environments/globals, ordered merges, root boundaries, CLI plugin precedence, and type-aware batching/SFC paths. Batching payloads and severities use the existing executable-fixture approach; syntax assertions use real OXC.
• The initial additional integration run passed 38/39 tests. Investigation found a stale about:blank assertion: the browser runner intentionally loads its own generated file URL, not another test's page. The test-only correction landed in Unify asset build preparation and supervised development sessions #37 as e6ed03e, where all 39 integration tests pass. This refreshed branch includes that correction; its lint diff remains unchanged.