Publish builds to a branch instead of to releases.

Releases and version numbers are gone. CI now rebuilds all three platforms
on every change to main and commits the packages to the `builds` branch,
so what anyone downloads is the current state of the repository. The
branch is rewritten from scratch each time rather than added to, so the
repository keeps one copy of the packages instead of a ~70 MB set per
commit.

Without tags there is no version to compare, so a build carries the
commit it was made from and the branch carries a VERSION file naming the
same commit. The updater fetches those few bytes and treats any
difference as being behind; commits are not ordered, and the branch only
ever holds the current build.

The installers fetch from the branch over raw.githubusercontent.com for
the same reason.

Co-authored-by: Cursor <cursoragent@cursor.com>

Makefile

@@ -17,12 +17,12 @@ GTK_LIBS   := $(shell $(PKG_CONFIG) --libs gtk4)
 CFLAGS = -Wall -Wextra -Wno-deprecated-declarations $(GTK_CFLAGS)
 LIBS = $(GTK_LIBS) -lm
 
-# Release builds pass the git tag (the CI workflow exports it), which bakes the
-# version into the binary for the updater to compare against. Without it the
-# build keeps the "dev" default from maturita.h and never offers an update.
-VERSION ?=
-ifneq ($(VERSION),)
-CFLAGS += -DAPP_VERSION='"$(VERSION)"'
+# Published builds pass the commit they were made from (the CI workflow
+# exports it), which the updater compares against the build in the repository.
+# Without it the build keeps the "dev" default and never offers an update.
+COMMIT ?=
+ifneq ($(COMMIT),)
+CFLAGS += -DAPP_COMMIT='"$(COMMIT)"'
 endif
 
 # Windows (MSYS2 / MinGW): .exe suffix, no console window, embed .ico.