Rename the project spec and update every reference to it

The charter file carried a tool-specific name while being the repository's own
document: mission, non-negotiable constraints, the pinned stack, repo
conventions and phase status, cited as authority by thirty files across the
agent, api, deploy, docs, search and terraform trees.

PROJECT-SPEC.md says what it is. All 42 references are updated in the same
commit, including the relative link in docs/status.md, so nothing points at a
filename that no longer exists.

ingest/README.md

@@ -43,7 +43,7 @@ database, regardless of any `tenant_id` tag a message carries -- routing
 a tagged record into its own tenant's dedicated database is
 `enterprise/internal/chwriter` and `enterprise/cmd/enterprise-ingest`'s
 job (a separate module by architectural convention, not a licensing
-split -- both are AGPLv3, see `/CLAUDE.md`'s licensing boundary), not
+split -- both are AGPLv3, see `/PROJECT-SPEC.md`'s licensing boundary), not
 this package's. `consumer` and `clickhousewriter` live outside
 `internal/` (moved there once `enterprise/internal/chwriter` needed to
 import them directly -- Go's compiler-enforced `internal/` visibility