refactor: extract @hyperframes/lint from core (#1756)

* refactor: extract @hyperframes/lint package from core

Moves all lint rules, hyperframeLinter, lintProject, and related types
from packages/core/src/lint/ into a new standalone packages/lint package.

Core keeps a thin re-export stub at @hyperframes/core/lint for backward
compatibility. Consumer imports (cli lint command, producer hyperframeLint)
are updated to import from @hyperframes/lint directly.

Depends on @hyperframes/parsers (PR #1755).

* fix: restore postcss-selector-parser in core (sourceMutation.ts still uses it)

* fix(ci): add parsers+lint to Dockerfile and build before preview tests

* chore: update bun.lock after restoring postcss-selector-parser dep

* test(cli): update lintProject test for string-dir signature from @hyperframes/lint

* refactor(core): single-source the lint engine in @hyperframes/lint

Delete core's byte-identical copy of the lint rule engine and re-point
staticGuard at @hyperframes/lint, so the render-time render-gate and the
studio preview share one rule engine instead of two copies that could
silently diverge. Back-compat preserved via the @hyperframes/core/lint stub.

Addresses review feedback on the dual-copy footgun.

packages/lint/src/index.ts

@@ -0,0 +1,9 @@
+export type {
+  HyperframeLintSeverity,
+  HyperframeLintFinding,
+  HyperframeLintResult,
+  HyperframeLinterOptions,
+} from "./types.js";
+export { lintHyperframeHtml, lintMediaUrls } from "./hyperframeLinter.js";
+export { lintProject, shouldBlockRender } from "./project.js";
+export type { ProjectLintResult } from "./project.js";