Migrate build system from autotools to CMake

Replace configure.in + 7 Makefile.am files with a CMake build:
- Top-level CMakeLists.txt with feature detection (SDL 1.2,
  SDL_image, OpenGL, optional OSS/ALSA), platform-specific install
  layouts (macOS .app bundle, Windows simple bundle, Unix), and a
  shared kobo_deps INTERFACE target for flags and link libraries.
- Sub-CMakeLists for graphics/, sound/, eel/ static libraries.
- aconfig.h.cmake.in and Info.plist.cmake.in templates (minimal:
  only the HAVE_* macros actually referenced by the code).

Remove all autotools machinery: configure, configure.in, aclocal.m4,
Makefile.am files, generated Makefile.in files, install-sh, missing,
depcomp, compile, mkinstalldirs, config.guess, config.sub, the
buildpkg.sh Solaris helper, and the cfg-* configure shortcuts.

Update .gitignore for CMake out-of-tree builds, and point
run-kobodl.sh at build/kobodl (overridable via KOBODL_BIN).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

.gitignore

@@ -1,22 +1,15 @@
-# Build artifacts
-*.o
-*.a
-*.lo
-*.la
-.deps/
-.libs/
+# CMake build outputs
+build/
+build-*/
+CMakeCache.txt
+CMakeFiles/
+cmake_install.cmake
+CTestTestfile.cmake
 
-# autotools generated state (regenerated by configure)
-Makefile
-!data/gfx/Makefile.am
-!data/sfx/Makefile.am
-autom4te.cache/
-config.log
-config.status
-stamp-h1
-Info.plist
+# Editor / OS detritus
 *~
+.DS_Store
 
-# Local build outputs
-kobodl
+# Runtime logs
 log.txt
+log.html