Extract the wrapping text-entry popup and put quick-create and link-PR on it

[MJohnson459]

Three modal arms in crates/voro/src/ui.rs drew a single typed buffer into a
bordered popup, but only Mode::Prompt sized the box from the wrapped line
count. Mode::LinkPr and Mode::QuickCreate asked popup_area for a fixed
three rows, two of them borders, so everything past the first wrapped row — the
▏ cursor included — was clipped: the operator typing a long intent into n, or
pasting a long PR URL, was typing blind.

What changed

The prompt's body is now draw_text_entry_popup(frame, title, buffer), sitting
beside popup_area as part of the same popup toolbox. It splits the buffer on
'\n', appends the cursor to the last line, builds a wrapping Paragraph,
measures it with line_count at the popup's inner width, sizes the box
rendered_rows.clamp(3, 20) and past the clamp scrolls to the tail. Width 72,
the clamp and the tail scroll are the prompt's numbers unchanged, now named as
WIDTH/MIN_ROWS/MAX_ROWS constants. Both explanatory comments — the
'\n'-vs-wrapped-count note and the RejectWork multi-line one — moved across
with the code they describe.

All three arms call it and are one line each plus their title, which each
passes whole because the suffixes genuinely differ ("⏎ to submit" for the
prompt and link-PR, "⏎ to propose" for quick create). Mode::QuickCreate still
resolves the project name from app.projects exactly as before,
unwrap_or("the project") and all. No copy of the measure/clamp/scroll block
survives. The helper takes no hits and pushes nothing, so the arms still
register no click target.

Key handling is untouched — App::key_quick_create and key_link_pr are not
in the diff. Mode::AddProject and the viewer form are deliberately left
alone: two-field forms with focus styling are a different shape, and bending
the helper to fit them was out of scope. Nothing in DESIGN.md needed changing;
this was a rendering defect, not a change to documented modal semantics.

Verification

Two new tests mirror the existing prompt pair over Mode::QuickCreate:
quick_create_popup_grows_with_wrapped_text and
quick_create_popup_scrolls_to_the_tail_when_it_overflows. render_prompt was
generalised into render_modal(store, mode) with thin render_prompt /
render_quick_create wrappers, the quick-create one seeding
store.create_project("voro", "/tmp/voro") before App::new so the title
resolves. I confirmed both new tests are load-bearing by temporarily restoring
the old three-row arm — both fail against it, then pass again with the helper.
prompt_popup_grows_with_wrapped_text and
prompt_popup_scrolls_to_the_tail_when_it_overflows pass unchanged.

cargo test --workspace (470 + 389 + 1, 0 failed), cargo clippy --workspace --all-targets -- -D warnings and cargo fmt --all are all clean.

Manually driven through the verify skill against a scratch db in tmux at
110x30. Pressing n with one project goes straight to quick create; typing
~130 columns wrapped to two rows with TAILMARK▏ visible, and typing on past
the clamp pinned the tail and cursor on the last row while the head scrolled
out of the 20-row box. g on a non-review task opened the link-PR prompt,
where a 116-character URL wrapped across two rows with the cursor visible —
both previously clipped. The refine popup still renders exactly as before.