docs: standardize Markdown paragraph wrapping across the repository #5449

User Story

As an OpenShell contributor reviewing #5260, I need Markdown paragraph wrapping to be consistent so small guidance changes do not introduce formatting churn or require repeated review corrections.

Description

Standardize Markdown paragraph wrapping across the repository. Establish a documented convention, reconcile existing guidance and formatter behavior, and apply the agreed style in a dedicated change. Preserve Markdown structure, code blocks, lists, tables, and rendered meaning.

Until that work is done, match the existing style of each file being edited rather than reformatting unrelated Markdown files.

Context

Review of #5260 found hard-wrapped additions in .agents/skills/create-github-issue/SKILL.md and .agents/skills/triage-issue/SKILL.md, whose existing prose uses single-line paragraphs. Those two additions are being corrected in #5260. Broader cleanup, including other PR-creation guidance, is deliberately deferred to this issue.

Definition of Done

• Document a consistent paragraph-wrapping convention and any justified exceptions.
• Align applicable formatter/linter configuration and contributor guidance with that convention.
• Apply the convention across the agreed repository scope in a separate, reviewable formatting change.
• Preserve prose content and rendered structure, and run the applicable Markdown checks.