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.

.fallowrc.jsonc

@@ -267,6 +267,18 @@
       "packages/parsers/src/gsapWriterParity.acorn.test.ts",
       "packages/parsers/src/htmlParser.roundtrip.test.ts",
       "packages/parsers/src/htmlParser.test.ts",
+      // @hyperframes/lint rule test files: parallel arrange/act/assert test cases
+      // (pre-existing structure from when lint lived in packages/core/src/lint/).
+      "packages/lint/src/rules/adapters.test.ts",
+      "packages/lint/src/rules/captions.test.ts",
+      "packages/lint/src/rules/composition.test.ts",
+      "packages/lint/src/rules/core.test.ts",
+      "packages/lint/src/rules/fonts.test.ts",
+      "packages/lint/src/rules/gsap.test.ts",
+      "packages/lint/src/rules/media.test.ts",
+      "packages/lint/src/rules/slideshow.test.ts",
+      "packages/lint/src/rules/textures.test.ts",
+      "packages/lint/src/hyperframeLinter.test.ts",
       // slideshowPanelHelpers.ts: setSlideNotes/addFragment/addHotspot share an
       // intentional parallel shape (signature + mapSlidesIn → exists-check →
       // map/append); the per-slide mutation differs, so a shared abstraction
@@ -311,6 +323,13 @@
       "packages/parsers/src/htmlParser.ts",
       // executeGsapMutation (CRITICAL) pre-dates this PR; studio-api still lives in core.
       "packages/core/src/studio-api/routes/files.ts",
+      // lint rule implementations and project linter: pre-existing complexity
+      // (moved from packages/core/src/lint/). File-level exemption avoids the
+      // line-shift fingerprint problem for inherited findings.
+      "packages/lint/src/rules/media.ts",
+      "packages/lint/src/rules/textures.ts",
+      "packages/lint/src/rules/gsap.ts",
+      "packages/lint/src/project.ts",
       // SlideshowPanel.tsx: top-level editor panel that wires several independent
       // sections (slides/inspector/branches/hotspot). Its cyclomatic count comes
       // from that fan-out; splitting it would scatter shared state without
@@ -329,7 +348,7 @@
       // generated table's shape test; this is dev tooling, not shipped runtime.
       "packages/cli/scripts/sync-agent-dirs.ts",
       // Files modified only for import-path updates (one-line changes to switch
-      // from @hyperframes/core/* subpaths to @hyperframes/parsers). Their complexity
+      // from @hyperframes/core/* subpaths to the new packages). Their complexity
       // is pre-existing; the line-shift fingerprint problem makes fallow treat
       // the violations as new even though no logic changed.
       "packages/core/src/core.types.ts",
@@ -338,6 +357,10 @@
       "packages/studio/src/hooks/gsapShared.ts",
       "packages/studio/src/hooks/gsapDragPositionCommit.ts",
       "packages/studio/src/hooks/gsapKeyframeCacheHelpers.ts",
+      "packages/cli/src/commands/lint.ts",
+      "packages/cli/src/commands/preview.ts",
+      "packages/cli/src/commands/publish.ts",
+      "packages/cli/src/server/studioServer.ts",
       // set-version.ts: compareSemver helper has pre-existing complexity from
       // semver string parsing logic; line-shift fingerprint problem from new
       // packages added to PACKAGES array makes fallow treat it as new.