AQ2 JMod maintenance and puppet demo stability update

Consolidated update from the original uploaded source through the current v6 source package

Reworked the old Linux-only Makefile into a cleaner multi-target build layout.
Added separate build modes for normal, debug, release and sanitizer builds.
Moved object files into a build directory instead of leaving them loose in src.
Added print-config, clean, distclean and install-oriented targets.
Added a Win64 cross-compile target intended to produce gamex86_64.dll.
Made AQTION_EXTENSION opt-in instead of enabled by default, avoiding accidental game API version 4 builds when the server expects version 3 or 3302.
Replaced the original aggressive optimization flags with safer debug-friendly defaults: -O2 -g -fno-omit-frame-pointer -fcommon.
Added stronger warning flags to expose unsafe old C patterns.

Fixed a severe memory corruption bug in CreatePuppetDemoFile() where an integer player number was accidentally passed as the destination pointer to sprintf.
Added safer client index handling for puppet demo filenames and player demo IDs.
Hardened puppet demo file command parsing so missing command tokens no longer become unsafe sprintf() or strtok() inputs.
Fixed unsafe file write formatting in puppet demo load/save paths.
Replaced direct atof() / atoi() parsing in puppet demo playback with NULL-safe parsing wrappers.
Fixed the confirmed crash where FollowPuppetDemoFile() called atof(NULL) while playing a puppet demo.
Added handling for blank, metadata and short lines in puppet demo playback so footer data does not crash the server.
Confirmed via core dump that the crash path was FollowPuppetDemoFile() → atof(NULL) from puppet think/frame processing, then patched that path directly.

Fixed .pdm metadata parsing for footer lines like info Author:playername JMod:1.23.
Fixed the load/play display showing Author:Unknown even when the .pdm file contained a valid author footer.
Preserved support for older info/footer formats where possible.
Fixed the Pup and Time display collision caused by repeated use of AltString()’s static buffer in the same snprintf() call.
Made AltString() safer by avoiding uncontrolled writes and handling NULL input.

Replaced several unsafe sprintf() calls with bounded snprintf() or direct null termination.
Replaced zero-length sprintf(buffer, "") calls with buffer[0] = '\0'.
Fixed format string vulnerabilities such as passing user/file strings directly as format strings.
Replaced old FOFS/STOFS/LLOFS/CLOFS pointer-to-integer offset macros with offsetof().
Fixed undefined pointer increment expressions such as cur = cur++ and ent->client->chase_target = ent++.
Fixed an accidental assignment in a condition, if (max = 16), changing it to an actual comparison.
Replaced several float uses of integer abs() with floating-point absolute value handling.
Replaced the strict-aliasing-unsafe Q_fabs() implementation with a safer implementation.
Initialized puppet direction vectors before use in puppet look/aim code.
Added safer appending for small fixed-size display buffers.

Fixed the initial game library version mismatch caused by building with -DAQTION_EXTENSION.
Confirmed the rebuilt game library loads under the expected game API version when AQTION_EXTENSION is not enabled.
Confirmed puppet demos no longer crash after activation in the tested server setup.
Improved resilience when puppet demo playback reaches metadata/footer lines rather than movement-frame lines.