Fix Rowan examples for SDK 3.1.13

[aubcake]

Summary

Update the Rowan skill for the current rowan-python 3.1.13 API and bump the skill from v1.4 to v1.5.

• construct rowan.Molecule objects for workflows that reject bare SMILES
• correct descriptor semantics and verified aspirin values (MW is exact mass; TopoPSA is topological PSA)
• replace stale workflow names, keyword arguments, result properties, and project/folder lookup examples
• document the actual exception model (ValueError, httpx.HTTPStatusError, rowan.WorkflowError)
• fix webhook-secret return types and signature-verification parameters
• repair the end-to-end example, including its undefined top_compound variable

Validation

• Live API smoke tests:
  • rowan.whoami() authenticated successfully
  • aspirin descriptors completed: MW=180.042, SLogP=1.31, TopoPSA=63.6
  • phenol starling pKa completed: strongest_acid=9.995
• Static SDK audit over all six Rowan docs:
  • 33 referenced rowan.* symbols resolve
  • every documented rowan call uses keywords accepted by its 3.1.13 signature
  • Python fences parse and stale API patterns are absent
• uv run skills-ref validate skills/rowan — pass
• uv run --with pytest python -m pytest tests/_meta -q — 10 passed, 1,213 subtests passed
• git diff --check — pass

The optional Cisco skill scanner was not run locally because SKILL_SCANNER_LLM_API_KEY was not configured; repository PR scanning can cover it.