Overall visual and information-density redesign of the PR review comment

[JSONbored]

Part of #5095.

Context

Even after the other 5 sub-issues in this epic land (slimmer signals table, cut/redesigned "Contributor next steps", terser Improvement row, distinguished BETA section, possible fix-suggestion codeblocks), the comment as a WHOLE hasn't had a real design pass -- it's grown feature-by-feature, each addition reasonable in isolation. Maintainer ask, verbatim: "something potentially more stylish/unique, and maybe a bit less text heavy / better designed."

Requirements

• Look at the comment holistically, AFTER the other sub-issues' changes land (this issue depends on Visually distinguish BETA/experimental review-comment features from stable ones #5096/Audit and redesign (or cut) the 'Contributor next steps' collapsible #5097/Slim and redesign the main PR signals table (cut low-value rows, redesign Gittensor context, explore Points Forecast) #5100/Simplify the 'Improvement' signal row to a terse score instead of a text wall #5101 being far enough along to know the actual final content, not the current bloated version) -- headers, spacing, table vs. non-table layout choices, where collapsibles vs. always-visible content makes sense, icon/emoji usage consistency, overall length.
• Consider information hierarchy explicitly: what MUST be visible without expanding anything (the verdict, the blocking reasons) vs. what's fine behind a collapsible for someone who wants detail.
• GitHub markdown constraints apply (no custom CSS/JS -- this renders in a plain GitHub comment): work within <details>, tables, headers, emoji, and markdown formatting only.
• Must stay within this codebase's existing public-safety constraints (sanitizePublicComment, forbidden-term guards) -- a visual redesign must not accidentally leak private wording through new formatting.

Deliverables

• 2-3 concrete full-comment mockups (real markdown, rendered) showing meaningfully different visual directions -- not just "make it prettier" in the abstract.
• A specific list of what changes (structure, ordering, always-visible vs. collapsed) and why, tied back to the earlier sub-issues' findings.
• Implementation of whichever direction the maintainer picks, with full test coverage and byte-identity preserved for any repo that hasn't opted into anything new.

Expected outcome

A review comment that reads as a deliberately-designed product surface, not an accretion of independently-shipped features -- shorter, clearer, and visually distinctive.

Open questions for the maintainer

• This is the most subjective sub-issue in the epic -- present real alternatives with actual rendered examples, don't just describe a vision and implement it unilaterally.

[linear-code]

JSO-3672