fix(rules): blank-line separate multiple-choice options (#246)

[gluefactory]

Summary

Closes #246.

Per the CommonMark spec, a soft line break renders as a single space. So
the multiple-choice template used in question-format-guide.md —

A) Option A
B) Option B
C) Option C

— collapses into one paragraph (A) Option A B) Option B C) Option C) in
strict renderers (IntelliJ, PyCharm preview, VS Code without the GFM
setting). Most AI-DLC users are in those exact IDE-driven workflows, so
this hits in the common case.

Changes

• Insert blank lines between options across the template and every file
  that follows it:
  • aidlc-rules/aws-aidlc-rule-details/common/question-format-guide.md
    (template + all in-page examples)
  • aidlc-rules/aws-aidlc-rule-details/common/session-continuity.md
  • aidlc-rules/aws-aidlc-rule-details/extensions/security/baseline/security-baseline.opt-in.md
  • aidlc-rules/aws-aidlc-rule-details/extensions/testing/property-based/property-based-testing.opt-in.md
  • docs/WORKING-WITH-AIDLC.md
• Add a guard rail: a new CI step (alongside markdownlint) fails when
  any two consecutive lines both match ^[A-Z]\) without a blank-line
  separator. Scope mirrors .markdownlint-cli2.yaml ignores so behavior
  is consistent with existing markdown CI.

Out of scope (intentional)

Two evaluator golden files under scripts/aidlc-evaluator/test_cases/
still use the old format. They are excluded from the CI scope (same as
markdownlint's ignore list) and left untouched to keep this PR focused.

Test plan

• Manual test on Claude Code (Linux): installed the rules from
  this branch into a fresh project per the README's "Claude Code —
  Option 1" instructions, then drove the workflow far enough to
  generate a clarifying-questions file. Opened it in PyCharm's
  Markdown preview (strict CommonMark) and confirmed each option
  renders on its own line. Before this fix, the same flow produces
  the collapsed-paragraph behaviour described in [Bug]: Question-format template renders as a single paragraph in strict CommonMark renderers (IntelliJ/PyCharm preview, etc.) #246.
• Regression guard: the new CI step failed on main's content
  (38 offending option-line pairs across 5 files) and passes after
  the fixes in this PR.
• No new lint regressions: markdownlint-cli2 continues to pass
  cleanly across 43 in-scope files locally.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of the project license.

[harmjeff]

LGTM! Clean fix for a real usability issue that hits users in the common case (IDE-driven workflows with strict CommonMark rendering).

Highlights:

• Correct approach per CommonMark spec — blank lines between options is the proper way to ensure they render as separate lines
• CI guard (awk regex check) is smart and scoped consistently with existing markdownlint ignores
• Good decision to leave evaluator golden files out of scope to keep the PR focused
• Thorough test plan (manual PyCharm verification + regression guard catching 38 existing offenders)

No concerns — approve.

[mayakost]

LGTM