chore: drop the dev-agent scratch report that rode into main with #616

[lis186]

摘要（繁中）

REPORT-611.md 是 #611 實作端的驗證報告草稿，隨 #616 誤入 main。派工 prompt 明寫「untracked is fine」，但沒有任何機制保證，我也沒在 commit 前查——所以它被一起 commit 了。本 PR 刪除它，並加上 REPORT-*.md 到 .gitignore，讓那句話由結構保證而非靠 agent 記得。

Why remove rather than keep

• Nothing references it: grep -rn 'REPORT-611' --include='*.{js,json,md,sh}' returns zero outside the file itself.
• Its content is already in the PR body of feat(index): per-session Claude launch account snapshot (accountEmail/accountDomain) #616 — guard-by-guard commands, exit codes, the explicit "not verified" list. The PR body is where a reviewer actually looks; a stray root-level markdown file invites the next reader to wonder whether it is maintained.
• It is a point-in-time scratch artifact, and two of its claims were already superseded during review (it reports a suite failure that does not reproduce in a clean env, and predates the two P2 fixes).

Second review

codex-exempt — deletes an unreferenced scratch file and adds one .gitignore
line. No source, no tests, no behaviour. Claiming a cross-model review ran would
be noise; the exemption is recorded so the merge hook sees a decision rather than
an omission.

Verification

• grep for references across *.js, *.json, *.md, *.sh: 0 outside the file.
• git ls-files --error-unmatch REPORT-611.md: tracked (so the deletion is real, not a no-op on an already-ignored path).
• Nothing imports or reads it, so no test can regress; the full suite is unchanged by construction.

Not verified: I did not re-run the full suite for a file-deletion-plus-gitignore change, since no code path can reach a root markdown file. CI covers it.