Move exitBasedOffOfValidationOutcome out of @finos/calm-shared into the CLI

## Feature Proposal

### Target Project:
`shared` (`@finos/calm-shared`) and `cli`.

### Description of Feature:
Move `exitBasedOffOfValidationOutcome` (which calls `process.exit`) out of `shared` into the CLI, where process management belongs, and drop it from the shared public API.

### User Stories:
- As a **shared maintainer**, I want no process-management code in the library, so every module in `shared` is browser-safe by default and the entry-point rules in `shared/AGENTS.md` hold without exceptions.
- As a **calm-server maintainer**, I want the library never to exit the process on my behalf.

### Current Limitations:
`shared/src/commands/validate/validate.ts` still exports `exitBasedOffOfValidationOutcome`, carrying its own `TODO - move this out of shared and into the CLI`. After #2880 it sits outside the browser graph (in the Node wrapper, not `validate-core.ts`), but it remains a Node-only function in a library that is otherwise engine-only. Its only caller is `cli/src/command-helpers/validate.ts`.

### Proposed Implementation:
- Add `exitBasedOffOfValidationOutcome` to `cli/src/command-helpers/validate.ts` (or a small `exit.ts` helper) and use it there.
- Remove the export from `shared` (`validate.ts` and `index.ts`). `shared` is `private: true`, so this is an in-repo change only; grep confirms no other consumer.
- Update `shared/AGENTS.md`'s entry-point rules to drop the `process.exit` caveat.

### Alternatives Considered:
Leave it — rejected: it is the last piece of process-management code in the library and the TODO has been open since the function was written.

### Testing Strategy:
Existing CLI validate specs cover the exit behaviour; shared tests and the browser-entry guard stay green; full workspace sweep.

### Documentation Requirements:
`shared/AGENTS.md` entry-point rules.

### Implementation Checklist:
- [ ] Design reviewed and approved
- [ ] Implementation completed
- [ ] Tests written and passing
- [ ] Documentation updated
- [ ] Relevant workflows updated (if needed)
- [ ] Performance impact assessed

### Additional Context:
Follow-up to #2880 / PR #3022 (deferred from its review).

Start with shared/src/commands/validate/validate.ts, cli/src/command-helpers/validate.ts, shared/index.ts, and shared/AGENTS.md. Grep for exitBasedOffOfValidationOutcome and run the existing CLI validate specs plus the shared browser-entry guard. Done means process-exit handling is owned by the CLI, the shared export and caveat are removed, and the workspace tests pass.

Written by the indexing model from the issue text.