fix(cli): fix endpoint example generation for global headers, nullable params, and recursive types

[iamnamananand996]

Description

Refs: Devin session
Requested by: @iamnamananand996

Three related fixes for endpoint example generation in the OpenAPI importer and IR generator:

1. Global header example failure drops all endpoint examples
When a global header's schema cannot produce an example (e.g. literal<2025-09-18> without quotes), ExampleEndpointFactory.buildEndpointExample returned an empty array for every endpoint, causing all userSpecifiedExamples to be dropped from the IR. Reported via polytomic/polytomic-python#9 — regression introduced in CLI v0.64.23 (2194f78).

2. hasExample() ignores nullable/optional wrappers
ExampleTypeFactory.hasExample() did not recurse into nullable or optional wrappers, silently dropping params that had examples inside those wrappers.

3. Recursive types cause cascading example failures
When cycle detection triggered in generateTypeReferenceExample (v1), it returned failure, which cascaded up and killed the entire parent example. Now generates minimal stub examples with leaf (primitive/enum/literal) properties filled in, so parent examples survive.

Changes Made

• ExampleEndpointFactory.ts: Removed the return [] early-exit when a global header example is null. The header is gracefully skipped instead — matching existing behavior for non-required regular headers.
• ExampleTypeFactory.ts: Added nullable and optional cases to hasExample() that recurse into the wrapped schema.
• generateTypeReferenceExample.ts: Replaced cycle-detection failure return with generateMinimalNamedExample() — a new function (~200 lines) that produces stub examples for objects (leaf properties only), enums (first value), aliases (resolve or empty object), and unions (first no-properties variant). Undiscriminated unions still return failure.
• generateTypeReferenceExample.test.ts: Updated existing cycle tests to expect stubs instead of failures; added new BulkSchedule-like 3-way cycle test case.
• Snapshots: Updated example-depth.json (stub left: {}, right: {} at cycle boundary) and simple-fhir.json (recursive FHIR types now produce stubs instead of empty examples).
• versions.yml: Single consolidated changelog entry for CLI v3.78.1.
• Updated README.md generator (if applicable) — N/A

Testing

• All 346 turbo tasks pass (compile + test)
• All seed test results pass (23 generators)
• git diff --exit-code CI check passes (snapshots committed)
• IR generator tests pass with updated snapshots (311 tests + 1 skipped)
• Manual verification with polytomic OpenAPI spec confirmed endpoint examples restored
• No dedicated test for the "unresolvable global header schema" path in ExampleEndpointFactory

Review Checklist

• generateMinimalNamedExample edge cases: The new stub generator handles objects, enums, aliases, and unions. Verify the logic for each branch, especially:
  • isLeafTypeReference intentionally returns false for lists/maps/sets — recursive containers get skipped in stubs
  • undiscriminatedUnion returns failure (could still cascade in some schemas)
  • Hardcoded maxDepth: 3 and skipOptionalProperties: true for leaf property generation within stubs
• Snapshot correctness: The simple-fhir.json diff is massive (~17M chars). Spot-check a few recursive types (e.g., Patient, Account, Script) to verify stubs look reasonable.
• Silent skip vs. warning: Null global header examples are silently skipped. Consider adding this.logger.trace(...) for debuggability.

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