docs(skill): guide agents through seeding comments correctly

[martintrojer]

This targets the second workflow the skill already names — agent review of a patch — where the agent files its findings into tuicr with review add and the human then opens the TUI to read them. The review lands on the diff, anchored to the lines it is about, instead of arriving as a wall of chat text the human has to map back onto the code themselves. They page through it with j/k, mark hunks reviewed, reply, delete the findings they disagree with, and export what survives. The human is reviewing the review, in the tool they already use for reviewing. That flow only works if the agent anchors comments to the right lines, and today nothing in the skill tells it how.

Three failure modes on that path. Each succeeds silently, so nothing steers away from it.

Reconstruct The Diff (new section). An agent needs the same diff the user sees before it can pick line numbers, and the slug says which one. Adds the scope-per-slug-segment table and the <base>~1 detail: range endpoints are inclusive, so diffing from <base> silently drops the first commit. Get this wrong and every line number is off, which is exactly how findings end up anchored to unrelated code.

--repo caveat (into Attach To A Session). [] with exit 0 also means "not a repo root" — a subdirectory returns it too. Read as "nothing open", an agent gives up while a session is running.

Verify seeded comments (into Add Agent Comments, next to the --input shape it depends on). A line past the end of the diff stores, prints back, and exits 0, but never renders — so the agent reports success on a review the human cannot see. Also: review comments reports no author, so the ids from add are the only way to tell agent comments from the user's later.

Test plan

• Field shapes read off src/review_cli.rs and exercised against the built binary: the documented flat --input form round-trips, an array is a parse error, path is not an alias for file
• Range recipe measured here. For commits/82e9508..b55e218, <base>~1..<head> gives 15 files / 306 insertions; <base>..<head> gives 9 / 155 — short by exactly commit 82e9508 (6 files / 151)
• [] exit 0 reproduced for repo root, subdirectory, and nonexistent path
• Out-of-range line reproduced: line 9999 in a 3-line file returns the stored comment, exit 0

[agavra]

Thank you @martintrojer for the contribution! This looks good to me.