refactor(#1294): T-final — delete the core.cjs re-export spine (epic #1267 complete) (#1295)

* refactor(#1294): T-final — delete the core.cjs re-export spine (epic #1267 complete)

After T0–T6 nothing imports core, so retire the spine and its scaffolding:
- delete src/core.cts (and the gitignored gsd-core/bin/lib/core.cjs artifact;
  remove its .gitignore + eslint-ignore entries)
- delete scripts/lint-core-spine-imports.cjs + its allowlist; drop it from the
  package.json lint:ci chain
- regenerate docs/INVENTORY-MANIFEST.json (drops the core.cjs surface)
- sweep stale references: CONTEXT.md glossary back-compat clauses (spine retired,
  callers import the leaf directly), planning-config.md CONFIG_DEFAULTS owner,
  and false present-tense core.cjs claims in leaf-module docstrings

The ADR-857 decomposition is complete: the former Core god-module is fully
dissolved into its leaf modules; no re-export spine remains. No behaviour change.

Closes #1294

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* fix(#1294): migrate the computed-path core.cjs importers the literal grep missed

bin/install.js used require(path.join(_gsdLibDir, 'core.cjs')) (a computed
path, and bin/install.js was never in the convergence lint's scan roots), and
~8 test files referenced core.cjs via path.join/readFileSync/existsSync/FILE_ARG
forms the literal-string migration grep missed. Route install.js's symbols to
their leaves (RUNTIME_PROFILE_MAP->model-catalog, resolveTierEntry/EFFORT_SET->
model-resolver) and repoint/adjust the test references to the leaves. Recovers
the 161 'Cannot find module core.cjs' failures from the spine deletion.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

gsd-core/references/planning-config.md

@@ -220,7 +220,7 @@ Squash merge is recommended — keeps main branch history clean while preserving
 
 ## Complete Field Reference
 
-Generated from `CONFIG_DEFAULTS` (core.cjs) and `VALID_CONFIG_KEYS` (config.cjs).
+Generated from `CONFIG_DEFAULTS` (configuration.cjs) and `VALID_CONFIG_KEYS` (config-schema.cjs).
 
 ### Core Fields