Remove stale core workspace package

[nahiyankhan]

Category: infrastructure
User Impact: Ghost contributors have one internal core source of truth while the public package exports stay unchanged.
Problem: The package flattening left a private @ghost/core workspace package beside the folded packages/ghost/src/ghost-core runtime. That duplicated source, kept stale workspace/build/test references alive, and made the repo shape harder to reason about.
Solution: Remove the stale workspace package, move its remaining tests into the unified public package test tree, point internal test imports at #ghost-core, and refresh package metadata/docs/lockfile to match. The flattening changeset now uses the repo's pre-1.0 minor-release convention.

Validation:

• pnpm typecheck: passed
• pnpm test: passed, 404 tests
• pnpm --filter @anarchitecture/ghost build: passed
• pnpm check:packed-package: passed
• pnpm check:terminology: passed
• pnpm check: passed
• pre-commit hook: passed pnpm check and format checks
• pre-push hook: passed pnpm build, pnpm test, and pnpm check

Changeset: added; .changeset/flat-ghost-package.md now marks the flattening package-shape change as minor for @anarchitecture/ghost.

Ghost Review:

• node packages/ghost/dist/bin.js check --base origin/main: passed with 0 findings
• node packages/ghost/dist/bin.js review --base origin/main: generated advisory review packet; packet diff was truncated because this PR deletes the old package tree, but no active deterministic failures were reported by ghost check

File changes

.changeset/config.json
Removed @ghost/core from ignored packages because the private package no longer exists.

.changeset/flat-ghost-package.md
Changed the release bump from major to minor.

README.md
Updated the repo layout table so packages/ghost is the single public package carrying the folded core runtime.

packages/ghost-core/package.json
Deleted the obsolete private workspace package manifest.

packages/ghost-core/src/
Deleted the duplicate private core source tree now folded under packages/ghost/src/ghost-core.

packages/ghost-core/tsconfig.json
Deleted the obsolete TypeScript project config.

packages/ghost-core/test/*.test.ts
Moved the remaining private core tests into packages/ghost/test/ghost-core/.

packages/ghost/test/gate.test.ts
Replaced the old @ghost/core test import with #ghost-core.

packages/ghost/test/ghost-core/*.test.ts
Preserved the moved core coverage under the unified package and updated imports to folded core exports; adjusted legacy grounding assertions to match the current warning-level contract.

pnpm-lock.yaml
Removed the packages/ghost-core workspace importer.

scripts/check-terminology.mjs
Removed stale scan roots for the deleted private package.

tsconfig.json
Removed the project reference to packages/ghost-core.

vitest.config.ts
Removed the @ghost/core alias that only existed for the stale private package tests.

Screenshots/Demos: N/A