feat: add non-triggerable sObjects reference to automation-flow-generate and platform-apex-generate skills

[berndmareth]

Summary

Adds a guardrail to the automation-flow-generate and platform-apex-generate skills so they check whether a target SObject supports Record-Triggered Flows / Apex triggers before running the generation pipeline, stopping early on known-unsupported objects instead of generating metadata that will fail to deploy.

Changes

• SKILL.md: added a "Record-Triggered flows — verify triggerability first" section instructing the pipeline to check the target object against references/non-triggerable-sobjects.md before generating, and to stop and explain if the object is unsupported.
• non-triggerable-sobjects.md (new): reference list of common standard objects that don't support Record-Triggered Flows (e.g. -LoginHistory, SetupAuditTrail, AsyncApexJob, ApexLog, *Share/*History objects, etc.).
• SKILL.md: added the same triggerability check to the Trigger authoring section, referencing its own references/non-triggerable-sobjects.md.
• non-triggerable-sobjects.md (new): equivalent reference list for Apex trigger generation.

Motivation

AI generation frequently attempts to create Apex triggers or Record-Triggered Flows on objects that don't support them (setup, audit, history, and log objects), producing metadata that fails deployment. This heuristic gives both skills an early, explicit check to catch obvious cases and avoid wasted generation attempts.

Notes

The reference lists are intentionally heuristic, not exhaustive — custom objects, managed-package objects, and new/changed standard objects per release may not be covered. Both docs state this explicitly.
No functional/pipeline code changed — this is skill documentation/reference guidance only.
Reviewers may want to sanity-check the object list for accuracy (e.g. UserRole is noted as "verify per org").

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @Bernd-Mareth-BDS to sign the Salesforce Inc. Contributor License Agreement.