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.

docs/status.md

@@ -2,7 +2,7 @@
 
 Phase-by-phase record of what was built, what "done" meant for each phase,
 and how it was verified. Conventions and constraints live in
-[`/CLAUDE.md`](../CLAUDE.md); the architecture spec is
+[`/PROJECT-SPEC.md`](../PROJECT-SPEC.md); the architecture spec is
 [`/docs/architecture.md`](architecture.md).
 
 Each phase has a runbook in this directory recording the actual