review(unified-comment): fix comments that overclaim what review.comment_verbosity: quiet drops

[JSONbored]

⚠️ Definition of Done: this issue must be completed in full, in a single PR. Do not split this
work across multiple PRs, and do not defer any Deliverable below to a follow-up issue. A PR that
satisfies only some of the Deliverables, stubs a required test, or leaves a checkbox
partially-done does NOT resolve this issue and will be closed.

Context

src/review/unified-comment.ts documents review.comment_verbosity: quiet's effect on the rendered PR
comment in two places, and both overclaim what quiet actually leaves untouched.

The UnifiedReviewInput.commentVerbosity field doc:

/** `review.comment_verbosity`: how much of the comment's collapsible detail renders. `quiet` drops the
 *  Nits collapsible and every `extraCollapsibles` section entirely (blockers/gate result/signals always
 *  stay — this only trims decorative detail, never the merge/close-relevant signal); `detailed` renders
 *  every collapsible pre-expanded (`<details open>`) instead of collapsed. `normal`/undefined (default) ⇒
 *  byte-identical to today. (#2047) */

An inline comment in the comment-building function itself:

// #6067: the old always-rendered 9-row table is split into an always-visible "Decision drivers" list
// (only rows that can move the verdict) and a collapsed "Context & advisory signals" fold (everything
// else). Like the table it replaces, NEITHER is gated by `review.comment_verbosity: quiet` -- these are
// gate-relevant/context signals, not decorative detail (matches the file's existing verbosity contract:
// only Nits + extraCollapsibles are ever dropped by `quiet`).

Both comments assert quiet drops only the Nits collapsible and extraCollapsibles sections. That claim
is directly contradicted a few lines below the second comment, in the same function, where THREE more
sections are explicitly gated on verbosity !== "quiet":

if (nonRequiredFailingChecks && verbosity !== "quiet") {
  blocks.push(details("Flagged checks (non-blocking)", nonRequiredFailingChecks, undefined, collapsiblesOpen));
}
// ...
if (satisfactionBody && verbosity !== "quiet") {
  blocks.push(details("Linked issue satisfaction", satisfactionBody, undefined, collapsiblesOpen));
}
// ...
if (thresholdBacktestBody && verbosity !== "quiet") {
  blocks.push(details("Threshold backtest", thresholdBacktestBody, "never blocks the verdict", collapsiblesOpen));
}

This is confirmed intentional, tested behavior (test/unit/unified-comment.test.ts around line 468 asserts
on quiet dropping these sections) — the comments were simply never updated as each of these three sections
was added over time (#4414-class advisory holds, #2174 linked-issue satisfaction, #8138 threshold
backtest), each one gated on quiet at the moment it was introduced without the earlier "only Nits +
extraCollapsibles" prose being revisited.

Requirements

• Both stale comments must be corrected to accurately list every section review.comment_verbosity: quiet
  actually drops today: the Nits collapsible, extraCollapsibles, "Flagged checks (non-blocking)", "Linked
  issue satisfaction", and "Threshold backtest".
• This is a comment-only fix — no change to which sections are actually gated on quiet, no change to the
  rendering logic itself, and no change to test/unit/unified-comment.test.ts's existing assertions (they
  already correctly test the real behavior; only the prose describing it is wrong).

Deliverables

• UnifiedReviewInput.commentVerbosity's field doc comment lists all five sections quiet drops
  (Nits, extraCollapsibles, Flagged checks (non-blocking), Linked issue satisfaction, Threshold
  backtest) instead of claiming only two.
• The inline #6067 comment above decisionDriverBlock/advisorySignalsTable no longer claims "only
  Nits + extraCollapsibles are ever dropped by quiet" — it's corrected to match the actual current set
  of five sections, or reworded to avoid enumerating a list that has already gone stale twice (e.g.
  pointing a future reader to grep for verbosity !== "quiet" as the authoritative list instead of
  restating it in prose).

Both Deliverables are required in the same PR.

Test Coverage Requirements

This is a comment-only change with no executable-code diff, so it does not add any new coverable lines/
branches under src/** and the Codecov patch gate has nothing new to measure here. Run the existing
test/unit/unified-comment.test.ts suite locally (including its quiet-verbosity assertions around line
468) to confirm no behavior changed.

Expected Outcome

A future reader of src/review/unified-comment.ts's review.comment_verbosity: quiet documentation gets an
accurate picture of everything quiet currently drops, instead of a stale list that undercounts by three
sections.

Links & Resources

• src/review/unified-comment.ts — the field doc (around lines 329-334) and the inline #6067 comment
  (around lines 911-915), plus the three verbosity !== "quiet" gates that contradict them (around lines
  907, 926, 934).
• test/unit/unified-comment.test.ts (around line 468) — the existing test already correctly covering the
  real behavior.

[linear-code]

JSO-7366