Merge master into StarForth-v4.0.0: the branch's build, master's CI files kept

For PR #30. master's 9 commits since the fork (T= board selection,
mk/boards.mk, build.yml, the nightly workflows) conflicted in four
files; each is resolved to the branch's version:

  .gitea/workflows/nightly.yml       added on both; master's copy named
  .gitea/workflows/nightly-docs.yml  the branch in its checkout, the
                                     branch's builds the default branch
  Makefile                           master's T= and mk/boards.mk against
  kernel/Makefile                    the branch's TARGET=<board> and
                                     boards/; master's edits were to
                                     Makefile.starkernel, renamed here

The two workflows' header comment now says they build master.

Merged cleanly from master: build.yml (its board matrix, Nexus publish
and 02:00 nightly; it still calls Makefile.starkernel and make
T=<board>, which this tree does not have -- #18) and mk/boards.mk
(nothing here includes it).

Against the branch the merge changes only those CI files and
mk/boards.mk: no kernel, v4 or Makefile source, so the build is the one
accepted on 2026-11-06.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GE3SDvQn5EoxdGufk84zz2

mk/boards.mk

@@ -0,0 +1,54 @@
+# Board target table — T= selects board, sets ARCH + BOARD + BOARD_NAME.
+# Included early by both Makefile and Makefile.starkernel, before arch
+# normalization runs. Each Makefile applies board-specific flag overrides
+# after its own arch block.
+#
+# Adding a new board: add an ifeq block here, then add compiler-flag
+# overrides in the board-override sections of Makefile and
+# Makefile.starkernel if the board needs tuning beyond the arch default.
+
+ifdef T
+
+ifeq ($(T),qemu)
+  ARCH          ?= amd64
+  BOARD         := qemu
+  BOARD_NAME    := QEMU x86_64
+  CROSS_COMPILE :=
+
+else ifeq ($(T),pc)
+  ARCH          ?= amd64
+  BOARD         := pc
+  BOARD_NAME    := x86_64 PC (native)
+  CROSS_COMPILE :=
+
+else ifeq ($(T),pi4)
+  ARCH          ?= aarch64
+  BOARD         := pi4
+  BOARD_NAME    := Raspberry Pi 4 (Cortex-A72)
+  CROSS_COMPILE := aarch64-linux-gnu-
+
+else ifeq ($(T),pi5)
+  ARCH          ?= aarch64
+  BOARD         := pi5
+  BOARD_NAME    := Raspberry Pi 5 (Cortex-A76)
+  CROSS_COMPILE := aarch64-linux-gnu-
+
+else ifeq ($(T),milkv)
+  ARCH          ?= riscv64
+  BOARD         := milkv
+  BOARD_NAME    := Milk-V Pioneer (SG2042 RISC-V 64)
+  CROSS_COMPILE := riscv64-linux-gnu-
+
+# ── Future boards (uncomment + add flag overrides in Makefile / Makefile.starkernel) ──
+# else ifeq ($(T),zynq7020)
+#   ARCH          ?= arm
+#   BOARD         := zynq7020
+#   BOARD_NAME    := Xilinx Zynq-7020 (Cortex-A9, 32-bit)
+#   CROSS_COMPILE := arm-linux-gnueabihf-
+#   # NOTE: requires removing the 32-bit guardrail and adding armhf toolchain support
+
+else
+  $(error Unknown board target T='$(T)'. Supported: qemu pc pi4 pi5 milkv)
+endif
+
+endif # ifdef T