dismissLatestBotApproval compares bot login case-sensitively, unlike every sibling bot-login check

[JSONbored]

Context

dismissLatestBotApproval in src/github/pr-actions.ts:130-161 finds the bot's own most recent APPROVE
review so it can be dismissed. It matches the bot's login with a case-sensitive ===:

const botLogin = `${env.GITHUB_APP_SLUG}[bot]`;
...
for (const review of batch) {
  if (review.user?.login === botLogin && review.state === "APPROVED") latestApprovalId = review.id;
}

(src/github/pr-actions.ts:135 and :143.)

Every other bot-login comparison in this same subsystem normalizes case before comparing:

• isLoopOverBotComment in src/github/comments.ts:104-106:

  function isLoopOverBotComment(comment: IssueComment, botLogin: string): boolean {
    return comment.user?.type === "Bot" && comment.user.login?.toLowerCase() === botLogin.toLowerCase();
  }

• src/github/self-authored.ts:23-29 (normalizeGitHubSlug) lowercases the app slug before every
  appSlugMatches comparison, and :36-40 (isBotActor) lowercases the actor login too.

If GitHub ever returns the bot's login with different casing than env.GITHUB_APP_SLUG produces (or the app
slug itself is configured with different casing than GitHub's canonical form), dismissLatestBotApproval
silently finds no match and returns { dismissed: false } — a quiet no-op with no error, not a crash, so it
would be easy to miss in practice: a stale bot approval would simply never get dismissed for a review-evasion
or re-review flow that expects it to be.

test/unit/github-pr-actions.test.ts:544-608 (the three dismissLatestBotApproval tests) only ever use a
review.user.login of "gittensory[bot]" against the default test-env GITHUB_APP_SLUG of "gittensory"
(test/helpers/d1.ts:85) — always matching case, so this gap is currently untested as well as unfixed.

Requirements

• dismissLatestBotApproval in src/github/pr-actions.ts MUST compare the review author's login to the
  expected bot login case-insensitively, matching the .toLowerCase() comparison pattern already used by
  isLoopOverBotComment in src/github/comments.ts:104-106.
• The fix must be scoped to the login comparison only (src/github/pr-actions.ts:143, and the derivation of
  botLogin at :135 if needed to support it) — no other behavior of dismissLatestBotApproval (pagination,
  the "latest across pages" selection, the best-effort try/catch, the dismissal write) may change.

Deliverables

• dismissLatestBotApproval in src/github/pr-actions.ts matches review.user?.login against the
  expected bot login case-insensitively.
• test/unit/github-pr-actions.test.ts extended with a case where a review's user.login uses different
  casing than env.GITHUB_APP_SLUG produces (e.g. "Gittensory[bot]" against the default
  GITHUB_APP_SLUG: "gittensory" from test/helpers/d1.ts:85), asserting the mismatched-case APPROVE
  review is still found and dismissed — mirroring the structure of the existing
  "dismisses the bot's own LATEST approve review..." test at test/unit/github-pr-actions.test.ts:544-566.

Test Coverage Requirements

This change touches src/github/pr-actions.ts and test/unit/github-pr-actions.test.ts, both under this
repo's src/** Codecov patch gate (99%+ patch coverage, hard gate). The new case-insensitive comparison
branch must be exercised by the new mismatched-case test so the patch is fully covered.

Expected Outcome

dismissLatestBotApproval finds and dismisses the bot's own latest APPROVE review regardless of the login
casing GitHub returns or GITHUB_APP_SLUG is configured with, matching the case-insensitivity already
guaranteed for every other bot-login check in this subsystem (comments.ts, self-authored.ts), instead of
silently degrading to a no-op on a casing mismatch.

Links & Resources

• src/github/pr-actions.ts:130-161 (dismissLatestBotApproval, the function to fix)
• src/github/comments.ts:104-106 (isLoopOverBotComment, the case-insensitive pattern to mirror)
• src/github/self-authored.ts:23-29, :36-40 (normalizeGitHubSlug / isBotActor, further precedent for lowercasing bot logins before comparison)
• test/unit/github-pr-actions.test.ts:544-608 (the existing dismissLatestBotApproval test block to extend)
• test/helpers/d1.ts:85 (default GITHUB_APP_SLUG test fixture value)

[linear-code]

JSO-4497