feat(k-ui): text_input (label above, app owns text via on_change, caret, erase, submit, secret, placeholder); keys Left/Right/Space/Char/Erase; settings app filter; apps 8-page stack (k-ui overflowed 16K), args page -> 0x1000

docs/ipc.md

@@ -78,7 +78,10 @@ A thread made by `SpawnThread`/`SpawnThreadIn` starts with the caller's
 the slots of the console, log and storage capabilities it was handed, and
 whether its parent put an arguments page at `ARGS_VA` (NUL-separated, the
 program's name first; the parent fills a page and `MapPage`s it over, so
-the program owns it and it goes when the program does).
+the program owns it and it goes when the program does). It sits at
+`0x1000`, above the unmapped page 0; the stack runs from just below the
+image (`0x10000`) down toward it: 4 pages for system programs unless init's
+table says more, 8 for apps.
 
 Boot loads only init and storage, both packed into the kernel image (they
 are what reads the disk, so they cannot come from it). The disk is one ext4