fix: explicit PRINTABLE_BINARY_MAP notice (Zig+FFI); drop stale PROJECT_STRUCTURE.md

The Zig and FFI builds use a compiled-in map and cannot honor a runtime
PRINTABLE_BINARY_MAP file (the C/Lua/Node builds load the map at runtime).
The audit flagged that both *silently* ignored it; now they print a one-line
notice pointing to the C/Lua/Node builds for custom maps. (Full runtime-map
support in the comptime-optimized Zig core is a larger deferred change.)

Also remove PROJECT_STRUCTURE.md (stale — listed test_all/test_wasm etc. that
no longer exist); per-file purpose docs will come from the dirtree pass.

Author: pmarreck

src/printable_binary_ffi_main.c

@@ -471,6 +471,9 @@ int main(int argc, char *argv[]) {
     const char *prog_name = argv[0] ? argv[0] : "printable-binary";
     bool stats_enabled = !env_var_truthy(getenv("PRINTABLE_BINARY_MUTE_STATS"));
 
+    if (getenv("PRINTABLE_BINARY_MAP") != NULL) {
+        fprintf(stderr, "Warning: PRINTABLE_BINARY_MAP is ignored by the FFI build (compiled-in map); use the C, Lua, or Node build for custom maps.\n");
+    }
     if (opts.help_mode) {
         print_usage(prog_name);
         return 0;

src/zig/main.zig

@@ -546,6 +546,14 @@ pub fn main(init: std.process.Init) !void {
         return;
     }
 
+    // The Zig build uses a compiled-in map and cannot honor a runtime PRINTABLE_BINARY_MAP
+    // file (unlike the C/Lua/Node builds). Say so explicitly instead of silently ignoring it.
+    if (g_environ_map) |env| {
+        if (env.get("PRINTABLE_BINARY_MAP")) |_| {
+            rawWriteAll(std.Io.File.stderr(), "Warning: PRINTABLE_BINARY_MAP is ignored by the Zig build (compiled-in map); use the C, Lua, or Node build for custom maps.\n");
+        }
+    }
+
     if (opts.mappings_mode != .none) {
         try printMappings(opts.mappings_mode);
         return;