feat(tui): the intro splash — mark, ring, and a tagline that types itself

[plombeer31]

Stacked on #222 (which is stacked on #220). Retarget as each merges.

Why

A first run opened on three unstyled option rows. The product's name appeared nowhere on the screen a new user meets first — the mark, the wordmark and the tagline all shipped in logo.tsx and none of them were used until the operator was already inside the app.

The screen

The mark inside a ring of smaller crosses, ATOMIC (the first 23 columns of the shipped ATOMIC AGENT wordmark), and TAGLINE — the string the codebase already carries — typing itself in at ~45 ms/char, then [ press any key to continue ].

                                                  ✛
                                         ✛                ✛
                                             ███████░
                                  ✛         ████████░░
                                           █████████░░           ✛
                              ✛   █████████████████████████████░    ✛
                                  █████████████████████████████░░
                              ✛              ██████████░░░░░        ✛
                                 ✛           ███████░░░
                                        ✛                ✛
                                      ▄▀█ ▀█▀ █▀█ █▀▄▀█ █ █▀▀
                                      █▀█  █  █▄█ █ ▀ █ █ █▄▄
                                        Local AI-First Agent
                                   [ press any key to continue ]
  ctrl+c quit

Three things worth reviewing

use-typewriter.ts runs one interval for the whole reveal. My first draft listed the revealed count in the effect's dependency array, so every character tore the timer down and armed a fresh one — with Ink's frame commit in between, a 45 ms/char reveal actually crawled at ~230 ms/char. The count advances inside the tick now and the timer stops itself on the last character. (Under ink-testing-library the rate is bounded by its ~4 fps commits regardless, which is why the test asserts progress-then-settle on a short string rather than a duration.)

The ring is an ellipse. A cell is ~2.2× taller than wide, so a circle drawn in cells reads as a wide oval. orbit-field.ts derives the vertical radius from CELL_ASPECT, clips to the viewport and to reserved bands, and dedupes cells that round onto each other.

Nothing is allowed to outgrow its rows. Ink 7 overlaps rather than clips, so an art block one row too tall does not get cropped — it paints over the lines above. intro-art.ts takes a row budget and sizes the ring by whichever runs out first, rows or columns; the mark steps md → sm → none by the rows actually left over rather than by the size tier; and the ring is dropped entirely if it cannot clear the mark's clear space (one arm width) instead of resting a cross against an arm.

Interaction

Any key finishes the reveal, a second key moves on — an animation nobody can interrupt is a wait, and one that vanishes on the key meant to hurry it is a screen nobody reads. The splash claims Esc too: it must not skip setup from a screen that has not yet said setup is what comes next. introSeenAt is stamped as the splash is dismissed, not at the end of the flow.

Verified in a PTY

• 100×30 — full ring, everything on screen, hints on the last row.
• 86×26 — ring dropped for clear space, mark + wordmark + tagline + advisory footer.
• 72×20 — sm mark with a small ring; the whole screen still fits.

Tests

orbit-field.test.ts (ellipse ratio, viewport clipping, dedupe, reserved bands), intro-art.test.ts (mark centred, height never exceeds budget, ring present / dropped by clearance, crosses never overwrite the mark), use-typewriter.test.tsx (progresses, settles, skip lands on the full string, empty string is done), and four new onboarding-screen.test.tsx cases including "two keys off the splash" and "Esc does not skip from the splash".

Full suite: 5169 passed; the two failures on this machine (fs-glob-real, send-message-concurrency) fail identically on main.