docs(spec): correct the stale cloud/environment.zod.ts attribution in the discovery-environment subset pin

The pin test's docblock told a reader that `EnvironmentTypeSchema` is declared
by `cloud/environment.zod.ts`, while the file's own import 28 lines below reads
`./discovery.zod`. `packages/spec/src/cloud/` was removed when the `./cloud`
subpath left `@objectstack/spec` (#16325, landed by #17372 / 776d64c) and
the enum was re-declared in `api/discovery.zod.ts:434`, where it lives today.

Two residues of that move are corrected, both prose:

- the declaration table row, now naming `api/discovery.zod.ts`, with one added
  sentence recording why both rows name one module — so the next reader does
  not read the repetition as a copy-paste slip;
- the reverse cross-reference note, which named the two carrier FILES; it now
  names the two DECLARATIONS, which is what the sentence is actually about and
  what survives the next move.

Re-derived rather than copied forward: both member lists are unchanged and
correct (`production sandbox development` / those three plus `test staging
preview trial`, `discovery.zod.ts:473` and `:434`), and the two folds the
docblock cites (`staging` -> `sandbox`, `test` -> `development`) match
`NODE_ENV_TO_DISCOVERY_ENVIRONMENT`.

No assertion, message or schema is touched.

Claude-Session: https://claude.ai/code/session_01JbZnqu8bt6YqfJsr9vaFb3
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

packages/spec/src/api/discovery-environment-subset.pin.test.ts

@@ -9,7 +9,10 @@
  * | declaration | members |
  * |:---|:---|
  * | `DiscoveryEnvironmentSchema` (`api/discovery.zod.ts`) | `production` `sandbox` `development` |
- * | `EnvironmentTypeSchema` (`cloud/environment.zod.ts`) | those three + `test` `staging` `preview` `trial` |
+ * | `EnvironmentTypeSchema` (`api/discovery.zod.ts`) | those three + `test` `staging` `preview` `trial` |
+ *
+ * Both rows name one module on purpose: #16325 removed the `./cloud` subpath
+ * and `EnvironmentTypeSchema` moved here with its only open-source reader.
  *
  * Keeping both is the ruled outcome, not a defect: discovery answers the coarse
  * question ("am I talking to production?") on a machine-readable surface whose
@@ -23,8 +26,9 @@
  * nothing referenced one enum from the other, so a rename or a removal on the
  * seven-member side would leave the three-member side silently claiming a
  * membership it no longer has. The prose cross-references now run both ways
- * (`discovery.zod.ts`'s `.describe()` since #4828; `environment.zod.ts`'s JSDoc
- * since this pin) — and prose is unassertable, which is what this file is for.
+ * (`DiscoveryEnvironmentSchema`'s `.describe()` since #4828;
+ * `EnvironmentTypeSchema`'s JSDoc since this pin, carried through the move) —
+ * and prose is unassertable, which is what this file is for.
  *
  * ⛔ Scope: this pins the RELATION only. It deliberately does not pin either
  * enum's exact membership — `EnvironmentTypeSchema` is free to grow a new