add embed contract for host integrations

[nahiyankhan]

Category: new-feature
User Impact: Applications can embed ghost's package loading, gather, pull, and material inspection behavior without shelling out to the CLI.
Problem: Host integrations currently have to parse CLI presentation output or reimplement package semantics, which risks drift in selection, ordering, material handling, and safety policy.
Solution: Add a model-free @design-intelligence/ghost/embed contract and make the CLI consume the same gather and pull primitives. The API exposes immutable snapshots, complete menus, validated pulls, host-policy material inspection, and pure observability event stamping while leaving persistence to the host.

Validation:

• pnpm check: passed
• pnpm test: 192 passed, 1 skipped
• pnpm build: passed
• packed-package import check: passed for @design-intelligence/ghost/embed

Changeset: added as a minor release for the new public subpath and host API.

ghost Review:

• ghost check --base origin/main: not available in this CLI version; deterministic repository checks passed via pnpm check
• ghost review --base origin/main --include-memory: not run because the repository has no .ghost/checks/ package and this CLI does not support --include-memory

File changes

.changeset/ghost-embed-contract.md
Records the new public embed capability as a minor release.

packages/ghost/README.md
Documents embed imports, semantics, inspection policy, markup safety, and host-owned observability persistence.

packages/ghost/package.json
Publishes the @design-intelligence/ghost/embed subpath.

packages/ghost/src/commands/gather-command.ts
Uses the shared embed gather result while preserving CLI formatting and event writes.

packages/ghost/src/commands/pull-command.ts
Uses the shared embed pull result while preserving CLI formatting and event writes.

packages/ghost/src/embed/gather.ts
Builds the complete, unfiltered guidance menu and explicit applicability contract.

packages/ghost/src/embed/index.ts
Defines the public embed exports.

packages/ghost/src/embed/inspect.ts
Adds policy-gated, contained local material inspection with declared-glob support and no network fetching.

packages/ghost/src/embed/pull.ts
Validates requested node ids, preserves steering order, transports materials, and extracts Skeletons.

packages/ghost/src/embed/readonly-map.ts
Provides a mutation-free map view for loaded snapshots.

packages/ghost/src/embed/snapshot.ts
Loads and freezes package, cover, glossary, node, and check state for hosts.

packages/ghost/src/embed/types.ts
Defines the public snapshot, gather, pull, inspection, and policy contracts.

packages/ghost/src/ghost-core/index.ts
Exports the material helpers needed by the embed implementation.

packages/ghost/src/ghost-core/material-transport.ts
Shares MIME and containment helpers, keeps text sniffing backward compatible, and prevents pull from following symlinks outside the repo.

packages/ghost/src/observability-events.ts
Adds a pure event-stamping helper and reusable event input types.

packages/ghost/test/cli.test.ts
Checks semantic parity between CLI JSON and embed gather and pull results.

packages/ghost/test/embed.test.ts
Covers snapshots, menus, pulls, inspection policy, globs, MIME and size limits, UTF-8 handling, containment, text compatibility, and events.

packages/ghost/test/public-exports.test.ts
Verifies the built embed subpath and public functions.

scripts/check-packed-package.mjs
Includes the embed subpath in packed-package import validation.

Screenshots/Demos: N/A