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.

terraform/internal/provider/provider.go

@@ -2,7 +2,7 @@
 // built on HashiCorp's terraform-plugin-framework (not the legacy
 // SDKv2 -- the framework is the actively-developed, currently-
 // recommended library for a provider started from scratch, matching
-// CLAUDE.md's "prefer boring, well-understood dependencies" read
+// PROJECT-SPEC.md's "prefer boring, well-understood dependencies" read
 // forward rather than backward).
 package provider