feat(cli): extract Obelisk runtime into npm package

Add @obelisk-apps/cli with the existing build, search, query, and attune contract plus official skill installation.

Separate the docs-only skill artifact, bootstrap installer, release layout, cross-platform CI, and package-level regression coverage.

docs/adr/0002-two-tier-runtime-contract.md

@@ -5,8 +5,8 @@ pin what "the contract" is so refactoring cannot silently change observable
 behavior. The four verbs (`build`/`search`/`query`/`attune`) are only the entry
 surface; agents actually depend on the *return shapes* of the sandbox helpers
 (`search`, `overview`, `memories`, …), which are already documented in
-`references/api-reference.md` and relied on by every example in
-`references/query-patterns.md`. Current behavior is good and there is no reason to
+`skill-doc/references/api-reference.md` and relied on by every example in
+`skill-doc/references/query-patterns.md`. Current behavior is good and there is no reason to
 change it during migration.
 
 **Decision.** Freeze the contract in two tiers. **Tier 1 (hard freeze, golden
@@ -16,8 +16,8 @@ read-only enforcement, `attune` exposing only `remember`/`forget`, the set of
 globals/helpers available inside `query`/`attune`). **Tier 2 (locked to
 api-reference.md):** each helper's documented return shape — not frozen forever,
 but never allowed to drift silently; contract tests assert the live shape matches
-`references/api-reference.md`, so changing a helper forces a doc change plus a
-deliberate version bump. `references/api-reference.md` is therefore promoted from
+`skill-doc/references/api-reference.md`, so changing a helper forces a doc change plus a
+deliberate version bump. `skill-doc/references/api-reference.md` is therefore promoted from
 description to authoritative contract, and Phase 1 becomes "make it authoritative
 and enforce it," not "write a new contract doc."