Add Nintendo DS port (Embedded Swift)

[colemancda]

Overview

Adds ports/NDS: a Nintendo DS homebrew port of ClassicUI built with Embedded Swift, modeled on MillerTechnologyPeru/swift-embedded-nds and junkbot-swift's ports/NDS — a Makefile-driven build targeting armv5te-none-none-eabi (an exact match for the DS's ARM946E-S), linked against calico-based libnds and packaged with ndstool using calico's prebuilt ARM7.

Both screens are 256×192: the bottom (touch) screen hosts the iPod UI through a software rasterizer drawn into a double-buffered 16bpp bitmap background (map-base flip, vblank-synced); the top screen shows a static controls banner in a second bitmap background.

Design

Same engine/port split as ports/3DS (#1): the desktop SwiftUI-subset core cannot compile under Embedded Swift (no Mirror, no any View existentials, no Foundation, no Observation), so the port uses the embedded mini-core — source/ClassicCore.swift and tools/gen_font.py are byte-identical to the 3DS port's, and source/Renderer.swift differs only in:

• screen size: 256×192 (7 visible menu rows instead of 9, same metrics)
• pixel format: ARGB1555 (red in the low bits, bit 15 = opaque) instead of RGB565
• present path: halfword copy into the bitmap background's VRAM instead of the 3DS's transposing shim

Everything else carries over: menus with selection restore and scroll windowing, settings value rows, Notes-style wrapped text pages, Now Playing with a live progress bar, the eased navigation slide with pinned status bar, and antialiased 8-bit-coverage text from the same build-time Helvetica rasterization.

common/shim.c carries the ARMv5TE runtime support the Embedded Swift object needs: posix_memalign, arc4random_buf, the _swift_stdlib_strto*_clocale wrappers, and the __atomic_* outline helpers (the ARM946E-S has no atomic instructions; a short IRQ lock makes each operation atomic with respect to interrupt handlers).

Once this and #1 both land, the shared embedded mini-core is a candidate for extraction into a common ports/ location.

Controls

Input	Action
D-pad up/down	rotate the click wheel
A	center button (select)
B	Menu (back), with the slide animation
X / Y	play/pause
L / R	previous / next track
START	exit

Building

export DEVKITPRO=/opt/devkitpro
export DEVKITARM=$DEVKITPRO/devkitARM
cd ports/NDS && make SWIFTC=/path/to/nightly/swiftc

Requires devkitPro with nds-dev, a Swift toolchain whose Embedded stdlib ships an armv5te-none-none-eabi slice (main-branch nightly snapshots; release toolchains only ship armv4t), and python3 with Pillow. Verified: builds a 175 KB ClassicUI.nds.

CI / Testing

• A Nintendo DS workflow builds the ROM on every push (devkitPro pacman + nightly Swift toolchain resolved at run time) and uploads ClassicUI.nds as an artifact — green, alongside the existing macOS/Linux jobs.
• Host-side snapshot renders of the 256×192 screens (main menu, Now Playing, song list) pixel-verified through the ARGB1555 path before the console build.
• Not yet run on hardware or in an emulator.