Review: batch line comments into one prompt for the session #119

Review surfaces can hand the session a reference today, never an instruction.
InjectMenu writes @path or path:12-30 into the terminal
(frontend/src/components/diff/InjectMenu.tsx:38), and a file's header adds the
whole file as context (FileDiff.tsx:99). Anything I actually want changed I
still type by hand, re-describing where it is while looking straight at it.

The rest of the category shipped the other half: read the diff, leave line
comments, batch them, hand them to the agent as one turn. Warp calls it
Interactive Code Review; Vibe Kanban feeds inline diff comments back to the
agent; JetBrains AIR does it; Zed has it as an open request
(zed-industries/zed#59157). lich already owns every piece except the batching.

Shape

• A comment is {path, lines, text}, anchored on the selection InjectMenu
  already resolves as lineRef.
• Comments accumulate for the review in front of me — the working tree
  (ReviewPanel) and a PR's changed files (PullsFiles).
• One action — Send N comments — renders them as a single markdown block and
  writes it into the PTY through the path the inject already takes
  (rpc.Terminal.Write → Service.Write, internal/terminal/terminal.go:356).
• Sending clears them.

Ceilings to accept up front

• It is text typed into a terminal. No structured protocol, no round trip, no
  resolved state coming back from the provider. That is the point: the harness
  types what I would have typed, in the order I read the diff.
• Anchors are line numbers in the diff as rendered. A comment written before the
  agent edits the file can point at a line that has since moved. Sending
  promptly keeps the window small; nothing tracks drift.

Open

• Where unsent comments live: in memory per panel, or persisted so switching
  tabs does not drop them.
• One widget for both surfaces, or the PR view first.
• Whether the composed prompt names files as @path and lets the provider read
  them, or pastes the hunks inline.
• Whether a comment on a PR file can also be sent to GitHub instead of to the
  session — same gesture, two destinations. Decide together with the review
  threads issue.