ci: reduce hosted Actions cost through scheduling

[quinnbot-ai]

Summary

• Schedule stock macOS Bash compatibility coverage only for relevant pull requests and a daily run.
• Remove duplicate post-merge full-suite validation while preserving all Ubuntu pull-request jobs.
• Keep Require no-mistakes lifecycle coverage and turn structurally impossible missing-marker states into notice/pass outcomes.

Verification

• Focused workflow contract and stock macOS Bash compatibility tests passed locally.
• Documentation check, ShellCheck-backed lint, and workflow validation passed.

Cost model

• Projected macOS savings: about 12.3 dollars per month at 50 percent path relevance.
• Projected duplicate-validation savings: about 78.7 dollars per month.
• Require no-mistakes signal correction: zero dollars direct runner savings.
• Path relevance is uncertain; daily macOS coverage is retained as the floor.