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>

TODO.md

@@ -740,32 +740,43 @@ Each was found by a test written to assert correct behavior.
     `tests/controller.c` passes -1 and -4096 to each.
 
 12. **A failed controller-DB fetch silently destroys the tracked fallback.**
-    `include/akgl/SDL_GameControllerDB.h` is committed deliberately so the
-    library still builds if upstream disappears. But `mkcontrollermappings.sh`
-    has no `set -e` and never checks `curl`'s exit status: on a failed fetch it
-    writes `mappings.txt` empty, then overwrites the good tracked header with
-    `AKGL_SDL_GAMECONTROLLER_DB_LEN 0` and an empty initializer — and exits 0.
-    Verified by pointing the script at an unresolvable host.
+    **Fixed in 0.5.0**, both halves.
 
-    Two compounding problems:
+    `mkcontrollermappings.sh` now runs under `set -euo pipefail`, fetches into a
+    temporary directory, and moves the result into place only after checking
+    three things: 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. `AKGL_CONTROLLERDB_URL` and
+    `AKGL_CONTROLLERDB_MIN_LINES` are environment-overridable, which is how the
+    failure paths were exercised.
 
-    - `add_custom_command` at `CMakeLists.txt:89-93` declares
-      `OUTPUT include/akgl/SDL_GameControllerDB.h` as a *relative* path, which
-      CMake resolves against the binary directory, while the script writes to
-      the source directory. The declared output never appears, so the command is
-      permanently out of date and re-runs on every build — making every build
-      depend on network access and leaving the file dirty in the working tree
-      each time.
-    - `const char *SDL_GAMECONTROLLER_DB[] = {\n};` is an empty initializer,
-      which is a constraint violation in ISO C and compiles only as a GCC
-      extension.
+    Verified against all five: an unresolvable host, a 404, a truncated
+    response, an 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.
+
+    The build no longer runs it. The `add_custom_command` declared
+    `OUTPUT include/akgl/SDL_GameControllerDB.h` as a *relative* path, which
+    CMake resolves against the binary directory while the script writes to the
+    source directory, so the declared output never appeared, the command was
+    permanently out of date, and every build re-ran it -- 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: `const char *SDL_GAMECONTROLLER_DB[] = {};`
+    is a constraint violation in ISO C that compiles only as a GCC extension,
+    and the minimum-count check is what guarantees at least one entry.
+
+    Regenerating against the real upstream produced byte-identical mappings --
+    2255 entries, no content change -- so the rewrite is faithful. The only diff
+    is the `$(date)` stamp and the include guard, which is
+    `_AKGL_SDL_GAMECONTROLLERDB_H_` now to match every other header. That change
+    was made in the generator rather than by hand, and the tracked copy carries
+    it so a future regeneration shows no spurious diff.
 
-    Fix: have the script fetch to a temporary file, check `curl`'s status and a
-    plausible minimum line count, and leave the existing header untouched on
-    failure (exiting non-zero). Separately, make regeneration explicit — a
-    dedicated `controllerdb` target, or an `OUTPUT` that matches where the
-    script actually writes — so an ordinary build neither needs the network nor
-    dirties the tree.
 13. **A stale build tree in the source directory breaks the coverage run.**
     `CMakeLists.txt:208` and `CMakeLists.txt:223` pass
     `--root "${CMAKE_CURRENT_SOURCE_DIR}"` to gcovr, and gcovr searches for