bootstrap: meson build, test harness, CI, conventions, README/AGENTS (et0)

Phase 0 (task et0): lays the build/test/CI/convention groundwork before any
feature code.

- meson.build: project ggaze C11 -Wall -Wextra; deps gtk4/glib/gio/libadwaita;
  feature options gegl/jxl/avif/heif (auto); generated ggaze-config.h with
  app id, version, GGAZE_HAVE_* feature flags.
- tests: GLib g_test harness with separate unit/integration suites
  (--suite unit / --suite integration); test_bootstrap sanity test proves
  the harness compiles and the config header is reachable; -Db_coverage=true
  coverage target wired.
- CI: .woodpecker/ci.yml three lanes (minimal, gegl, asan) with xvfb for the
  integration track and a coverage lane that warns until M10.
- conventions: .clang-format (3-space, 80-col, K&R, *-on-var, return type on
  its own line) + .editorconfig matching docs/coding-conventions.md; CI
  clang-format --dry-run -Werror gate.
- top-level README.md (humans) and AGENTS.md (agents) pointing into docs/.
- LICENSE (GPL-3.0-or-later), .gitignore, dir placeholders.

Acceptance: meson setup build && ninja -C build && meson test -C build green;
clang-format --dry-run --Werror clean.

1 files changed, 58 insertions, 0 deletions

diff --git a/.woodpecker/ci.yml b/.woodpecker/ci.yml
new file mode 100644
index 0000000..6ec4680
--- /dev/null
+++ b/.woodpecker/ci.yml
@@ -0,0 +1,58 @@
+# ggaze CI — Woodpecker (codeberg-native).
+#
+# Three lanes (see docs/IMPLEMENTATION.md Phase 0):
+#   minimal  all optional backends disabled; plain GdkPixbuf viewer.
+#   gegl     gegl=enabled (+ jxl/avif/heif auto) — keeps the optional path
+#            from bit-rotting.
+#   asan     minimal build under AddressSanitizer + UBSan (also drives the
+#            per-feature leak-check tasks).
+#
+# The coverage gate runs in the minimal lane and is "warn" until M10, after
+# which it is flipped to fail (see docs/IMPLEMENTATION.md Cross-cutting).
+
+matrix:
+  include:
+    - LANE: minimal
+      MESON_OPTS: "-Dgegl=disabled -Djxl=disabled -Davif=disabled -Dheif=disabled"
+      RUN_COVERAGE: "yes"
+      ENV: ""
+    - LANE: gegl
+      MESON_OPTS: "-Dgegl=enabled"
+      RUN_COVERAGE: "no"
+      ENV: ""
+    - LANE: asan
+      MESON_OPTS: "-Dgegl=disabled -Djxl=disabled -Davif=disabled -Dheif=disabled -Db_sanitize=address,undefined"
+      RUN_COVERAGE: "no"
+      ENV: "G_DEBUG=gc-friendly ASAN_OPTIONS=detect_leaks=1:abort_on_error=1"
+
+when:
+  - event: [push, pull_request, manual]
+
+steps:
+  build-and-test:
+    image: fedora:40
+    environment: ${ENV}
+    commands:
+      - dnf install -y --setopt=install_weak_deps=False
+          meson ninja-build gcc clang clang-format git
+          pkgconf-pkg-config xorg-x11-server-Xvfb
+          gtk4-devel glib2-devel libadwaita-devel
+      - |
+        if [ "$LANE" = "gegl" ]; then
+          dnf install -y --setopt=install_weak_deps=False gegl-devel babl-devel
+        fi
+      - meson setup build $MESON_OPTS
+      - ninja -C build
+      - clang-format --dry-run --Werror $(git ls-files '*.c' '*.h')
+      - |
+        if [ "$RUN_COVERAGE" = "yes" ]; then
+          # lcov/genhtml not installed in Phase 0 (gate warns until M10);
+          # add lcov + (perl-Dot-Graph or genhtml) here when M10 flips the
+          # coverage gate to fail.
+          meson setup -Db_coverage=true build-cov $MESON_OPTS
+          ninja -C build-cov
+          meson test -C build-cov
+          ninja -C build-cov coverage || echo "coverage: lcov/genhtml not installed (warn)"
+        fi
+      - meson test -C build --suite unit
+      - xvfb-run -a meson test -C build --suite integration
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