fix(permissions): restore /yolo off hint for default-source skip warning (CL-9385)

[TheGreatAxios]

Stacks on #1169 (owns the unified saved-skip warning); restores the in-session /yolo off hint for the default machine-wide settings source.

• When the active settings source is the default machine-wide file, the warning appends (/yolo off to re-enable)
• Custom-source warnings keep the file-path wording with no false provenance (byte-identical output)
• Tests pin both variants: helper unit tests, TUI wiring tests, exec stderr test

Verification

• RED: default-hint assertions failed on all three suites before the fix; custom pins passed
• bun run typecheck: exit 0
• bun run lint: exit 0
• bun run test (bun test ./src ./tests ./evals ./scripts --randomize --seed 424242): 8035 pass, 0 fail, exit 0

Fixes CL-9385

[linear-code]

CL-9385