Stop a failed controller-DB fetch from destroying the tracked fallback

Closes Defects -> Known and still open item 12, both halves.

include/akgl/SDL_GameControllerDB.h is tracked on purpose: it is the offline
fallback that keeps the library buildable when upstream is unreachable. The
script that writes it had no set -e and never checked curl, so a failed fetch
wrote AKGL_SDL_GAMECONTROLLER_DB_LEN 0 and an empty array over the good copy
and exited 0. The safety net destroyed itself, and because CMake re-ran the
generator on every build, an offline build was enough to do it.

The script now runs under set -euo pipefail, fetches into a temporary
directory, and moves the result into place only after checking curl's exit
status (with --fail, so an HTTP error is a status rather than an error page in
the body), a plausible minimum mapping count, and that no mapping carries a
quote or backslash that would break the C string literal it becomes. Any of
those failing leaves the tracked header exactly as it was and exits non-zero.

Verified against all five failure modes -- unresolvable host, 404, truncated
response, empty-but-successful response (the original failure exactly), and a
response containing a quote. Each refuses, and the header's checksum is
unchanged after every one. AKGL_CONTROLLERDB_URL and
AKGL_CONTROLLERDB_MIN_LINES are environment-overridable, which is how.

The build no longer runs it at all. The add_custom_command declared a relative
OUTPUT, which CMake resolves against the binary directory while the script
writes to the source directory, so the declared output never appeared and every
build re-ran the command -- needing network access and leaving the tree dirty.
It is an explicit `controllerdb` target now, and the header is no longer listed
as a library source, which is all it was there for.

The empty-initializer problem goes with it: an empty array initializer is a
constraint violation in ISO C that compiles only as a GCC extension, and the
minimum-count check guarantees at least one entry.

Also here, because it rested on a premise that turned out to be false: the
character suite is no longer excluded from CI's coverage and memory-check jobs,
nor from the mutation harness by default. It was excluded on the grounds that
it failed deliberately. It did not -- it was reporting success while running
one of its four tests.

25/25 pass, memcheck clean, shellcheck clean.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

scripts/mutation_test.py

@@ -24,7 +24,7 @@ Usage:
                         Default: all libakgl-owned C files under src/
     --work DIR          scratch dir for the mutated copy (default: a temp dir)
     --timeout SECONDS   per-suite ctest timeout (default: 120)
-    --exclude-test REGEX CTest regex to exclude (default: ^character$)
+    --exclude-test REGEX CTest regex to exclude (default: none)
     --threshold PCT     exit non-zero if mutation score < PCT (default: 0 = off)
     --list              only list the mutants that would be run, then exit
     --keep              keep the scratch working copy on exit (for debugging)
@@ -327,8 +327,10 @@ def main():
     ap.add_argument("--target", action="append", default=None)
     ap.add_argument("--work", default=None)
     ap.add_argument("--timeout", type=int, default=120)
-    ap.add_argument("--exclude-test", default="^character$",
-                    help="CTest regex to exclude (default: ^character$)")
+    # No default exclusion. This was "^character$" while that suite was
+    # believed to fail deliberately; it does not, and did not.
+    ap.add_argument("--exclude-test", default="",
+                    help="CTest regex to exclude (default: none)")
     ap.add_argument("--threshold", type=float, default=0.0)
     ap.add_argument("--junit", default=None,
                     help="write a JUnit XML report to this path")