feedback: plasma box, explicit fonts, and per-position text coalescing

Three endpoint gaps, found building the Descent 3 score overlay - the boxed
place|score field the original games drew over the callsign:

plasma box <x> <y> <w> <h> draws an outlined box with a blanked interior, the
overlay chrome, as one ESC P graphics write. The wire addresses whole bytes
horizontally, so the write covers the byte-aligned span containing the box and
clears span pixels outside it; documented, with 8-px alignment the advice.
Boxes queue FIFO with rows.

plasma text gains an explicit font: a third numeric token after the position,
with text still following, so `plasma text 2 2 7` still displays "7". Auto-fit
picks the font by LENGTH - short text always rendered large, and a "1" that
must fit a 12-px box simply could not be sent before. ResolvePosText
generalizes the legacy Score-font special case: 0 = auto, nonzero honored.

Text coalescing is now per position. The global rule - any queued text
superseded every other queued text - meant the documented two-field layout
(callsign top, score bottom) could not survive its own send burst: the second
field silently ate the first whenever both were queued. A newer text now
replaces only a queued text at the same (x,y).

15 new tests; 472 pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/OUTPUT-INTEGRATION.md

@@ -107,14 +107,22 @@ What the endpoint exposes (v1):
   position; the font still auto-fits by length. Use this to keep two fields on
   screen at once (e.g. callsign top line, score bottom line:
   `plasma text 2 2 "VIPER 1-1"` + `plasma text 2 18 "SCORE 4200"`).
+- **`plasma text <x> <y> <font> <text>`** — as above with an explicit font
+  (`2` small 5×7, `5` large 10×14, `0` auto). Auto picks the font by LENGTH,
+  so short positioned text always renders large; the explicit form is how a
+  short field ("1", "1000") fits inside a score box.
 - **`plasma clear`** — blank the display.
 - **`plasma row <y> <hex32>`** — one full 128-px bitmap row; see
   [Bitmap graphics](#bitmap-graphics-esc-p).
+- **`plasma box <x> <y> <w> <h>`** — outlined box, interior blanked: the
+  overlay chrome for a field drawn on top of other content (the original
+  games' rank|score box over the callsign). Byte-aligned horizontally — put
+  box edges on 8-px boundaries where neighbors matter.
 
 Text is **Latin-1** (one byte per char) — don't send UTF-8.
 
-Not exposed through the endpoint yet (small extensions when needed): explicit
-font/attribute selection and box draw/fill.
+Not exposed through the endpoint yet (small extensions when needed): text
+attribute selection (intensity/underline/reverse/flash) and filled-only boxes.
 
 ### Bitmap graphics (`ESC P`)