Rename to Finch, ONIT logo, random greeting, doc detail view

- App-wide rename Mike -> Finch in user-visible strings, system
  prompts, and tracked-change author. Internal types, file paths,
  and the mikeApi client name are unchanged.
- Brand logo swapped to assets/ONIT_Mark_Dark.svg (copied to
  frontend/public/onit-mark-dark.svg). Sidebar, header, and the
  initial assistant landing all use the static mark; MikeIcon stays
  in place for spinner / done / error status indicators.
- Initial assistant greeting now picks one of the work___ legal
  greetings at random per mount and substitutes the user's name.
- New 3-pane "doc detail" view in tabular review (TRDocDetailView):
  click a document filename in the table to drill into a 25/25/50
  layout - column list / cell value & explanation / DocView preview.
  Doc viewer wrapper is a flex container so DocView's flex-1
  scroll region resolves a real height (otherwise mouse-wheel and
  programmatic scroll were both dead).
- Inline cell editing in the doc detail middle pane: pencil-driven
  edit mode with textareas, Cancel + Save buttons, and a new
  PATCH /tabular-review/:reviewId/cells endpoint that stores the
  manually edited content and sets status to "done".
- In-doc search in the right pane: input + N/M counter + prev/next
  arrows. Multi-match highlighter walks the pdf-text-layer spans
  and wraps every occurrence in <mark.finch-search-match> with
  rgba background so the canvas glyphs underneath stay visible.
  Current match shown in orange, others amber. DocView's empty-quote
  effect now clears stale citation highlights so the search and
  citation paths don't fight over the same text divs.
- Top-bar prev/next document arrows so you can scan the same column
  across documents without going back to the table.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>