Give BASIC menus, dialogs and HUD labels over libakgl's UI helpers

Group K, and the first verbs to reach the akgl_ui subsystem 0.9.0 brought
in: MENU and GETMENU and RMENU, DIALOG, HUD and UISTYLE. A program that
wanted a title screen had to draw one out of CHAR and GETKEY, which is
what both breakout tutorials make a reader do.

The interesting part is the impedance mismatch. libakgl's UI is immediate
mode -- widgets are re-declared inside a frame bracket every frame and
clay borrows their text until the bracket closes -- and a BASIC program
says MENU 1, "START" on line 100 and expects it up on line 900, several
hundred frames later. So src/ui_akgl.c is retained on this side and
immediate on that one: the record's entry points are setters that copy
into akbasic_AkglUi, and akbasic_ui_akgl_render() replays the whole set
once a frame from the host's pump. No BASIC string, which lives in the
per-line value pool, is ever what clay is handed.

The shapes are borrowed rather than invented. MENU retires the way SOLID
does -- no entries retires one, no arguments retire them all. GETMENU
holds the step loop the way GETKEY does, so parking is not blocking: the
step still returns, the host keeps its frame rate, and the sprite, audio
and collision services keep running underneath because they run before
the blocking checks. RMENU(n,1) reads and clears the way BUMP() does.
Withdrawing the device or retiring the menu releases a holding GETMENU
with 0 rather than wedging the script, which is akbasic_input_service()'s
rule for a withdrawn keyboard.

One thing a program has to know, and docs/19-user-interface.md says it
twice: a menu that is up owns the cursor keys and Return. It has to, and
retiring it gives them back -- forget the MENU n before an INPUT and the
INPUT never sees the Return that ends it.

akbasic_runtime_set_ui() is its own function rather than a fifth argument
to akbasic_runtime_set_devices(), whose signature has twenty-eight call
sites in tests and documentation that are about something else.

deps/libakgl is not touched. akgl_UiAnchor has the four corners and dead
centre, so HUD offers exactly those five; TODO.md records what a
top-centre and bottom-centre would cost upstream, along with the three
other things this deliberately leaves out. No new error code either --
DEVICE, BOUNDS, SYNTAX and TYPE cover the group, and 520 stays free.

tools/screenshot.c had to learn that "needs a font" and "draws the text
grid" are two questions. They were one, and a UI figure came out black:
the text layer owns every pixel of the rows it covers and painted over
the widgets. The new ui=1 fence attribute asks for the first without the
second; MAINTENANCE.md documents it.

112/112 in both configurations, 112/112 under ASan and UBSan, coverage
94.1% against the 90% gate with src/runtime_ui.c at 99% of lines and
100% of functions, doxygen clean, and the four new figures byte-identical
on a re-render. TODO.md section 8's gate table was stale on several
counts besides these and is refreshed with measured numbers.

Co-Authored-By: Tachikoma (Claude Code Opus 5 1M) <noreply@anthropic.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EwxGB6TdoVvZ11KQQME9cL
Co-Authored-By: Andrew Kesterson <andrew@aklabs.net>

docs/11-verb-reference.md

@@ -32,6 +32,7 @@ for the reasoning in each case.
 | `DCLOSE` | `DCLOSE [n]` | Close channel `n`, or every channel. |
 | `DEF` | `DEF NAME(args) = expr` | Define a function. Multi-line definitions end in `RETURN`. |
 | `DELETE` | `DELETE [n][-n]` | Delete lines, with the same range forms as `LIST`. |
+| `DIALOG` | `DIALOG ["text"]` | Show a text panel across the bottom of the screen. No argument takes it down. See Chapter 19. |
 | `DIM` | `DIM A#(n [,...])` | Make an array. Subscripts start at zero; `n` is the count. |
 | `DIM` … `AS` | `DIM S@ AS T`, `DIM P@ AS PTR TO T` | Make a structure, or a strict pointer to one. See Chapter 16. |
 | `DIRECTORY` | `DIRECTORY` | **Refused.** Needs a directory-reading wrapper that does not exist yet. |
@@ -49,12 +50,14 @@ for the reasoning in each case.
 | `FOR` | `FOR V = a TO b [STEP c]` | Start a counted loop, ended by `NEXT`. |
 | `GET` | `GET V` | Take a keystroke if one is waiting, without stopping. |
 | `GETKEY` | `GETKEY V` | Wait for a keystroke, holding the program but not the host. |
+| `GETMENU` | `GETMENU n, V%` | Wait for a menu choice, holding the program but not the host. Assigns the entry number. See Chapter 19. |
 | `GOSUB` | `GOSUB line` | Call a subroutine, returning on `RETURN`. |
 | `GOTO` | `GOTO line` | Jump to a line or a label. |
 | `GRAPHIC` | `GRAPHIC mode | CLR` | Choose a screen mode, or clear it. |
 | `GSHAPE` | `GSHAPE A$, x, y` | Stamp a region saved by `SSHAPE`. |
 | `HEADER` | `HEADER "name"` | **Refused.** Formats a disk. |
 | `HELP` | `HELP` | Re-list the line the last error happened on. |
+| `HUD` | `HUD n [,anchor, "text"]` | Pin a line of text to a corner or the centre. No text retires the slot; no arguments retire them all. See Chapter 19. |
 | `IF` | `IF c THEN s [ELSE s]` | Branch. Everything after `THEN` belongs to the condition. |
 | `INPUT` | `INPUT ["prompt"] V` | Read a line from the user. |
 | `INPUT#` | `INPUT #n, V` | Read a line from a channel. |
@@ -65,6 +68,7 @@ for the reasoning in each case.
 | `LOAD` | `LOAD "name"` | The other name for `DLOAD`. |
 | `LOCATE` | `LOCATE x, y` | Move the pixel cursor. |
 | `LOOP` | `LOOP [WHILE c | UNTIL c]` | End a `DO` loop. |
+| `MENU` | `MENU [n [,"item", ...]]` | Show a menu the player picks from. No entries retires it; no arguments retire them all. See Chapter 19. |
 | `MOVSPR` | `MOVSPR n, ...` | Move a sprite. Four forms; see Chapter 8. |
 | `NEW` | `NEW` | Erase the program and every variable. |
 | `NEXT` | `NEXT V` | End a `FOR` loop and advance its counter. |
@@ -106,6 +110,7 @@ for the reasoning in each case.
 | `TROFF` | `TROFF` | Turn line tracing off. |
 | `TRON` | `TRON` | Turn line tracing on; each line prints its number in brackets. |
 | `TYPE` | `TYPE NAME` … `END TYPE` | Declare a record, its fields one per line. See Chapter 16. |
+| `UISTYLE` | `UISTYLE [fill, edge, ink [,pad [,radius]]]` | The one look every widget draws with. No arguments restores the default. See Chapter 19. |
 | `VERIFY` | `VERIFY "name"` | Compare the program in memory against a file. |
 | `VOL` | `VOL n` | Set the overall volume, 0 to 15. |
 | `WAIT` | `WAIT addr, mask [,xor]` | Poll a byte until it matches. Holds the program. |