Drop newlib printf: log via BDK s_vprintf, add debug.ini log switch

log_write was the only vsnprintf user and pulled in newlib's printf,
dtoa, malloc and soft-float code (~44 KB). The payload now fits the
RCM limit again (146800 -> 102801 bytes); the build fails if it grows
past it. debug.ini log=1 writes sd:/config/omninx/install.log.

source/install.c

@@ -289,7 +289,9 @@ int folder_copy_with_progress_v2(const char *src, const char *dst, const char *d
     install_set_color(COLOR_WHITE);
     
     // Perform the copy with progress updates
+    log_write("COPY TREE %s -> %s (%d Eintraege)\n", src, dst, (u32)total);
     res = folder_copy_progress_recursive(src, dst, &copied, total, start_x, start_y, display_name, &last_percent);
+    log_write("COPY TREE %s: %s\n", src, fs_error_str(res));
     
     // Final update - overwrite the same line
     gfx_con_setpos(start_x, start_y);
@@ -499,6 +501,7 @@ int delete_path_lists_grouped(const char *folder_display_name, ...) {
             res = f_unlink(path);
         }
 
+        log_write("DELETE %s: %s\n", path, fs_error_str(res));
         if (res == FR_OK || res == FR_NO_FILE)
             deleted++;
         else
@@ -1343,6 +1346,7 @@ static void install_extras_post_copy(void)
 }
 
 #define INSTALL_DEBUG_INI "sd:/config/omninx/debug.ini"
+#define INSTALL_LOG_PATH  "sd:/config/omninx/install.log"
 
 typedef struct {
     bool active;
@@ -1356,6 +1360,7 @@ typedef struct {
     bool skip_update_staging_cleanup;
     bool skip_update_horizon_oc;
     bool skip_hekate_8gb_post_copy;
+    bool log;
 } install_debug_opts_t;
 
 static void install_debug_load(install_debug_opts_t *d)
@@ -1397,6 +1402,8 @@ static void install_debug_load(install_debug_opts_t *d)
                 d->skip_update_horizon_oc = install_ini_kv_truth(kv->val);
             else if (strcmp(kv->key, "skip_hekate_8gb_post_copy") == 0)
                 d->skip_hekate_8gb_post_copy = install_ini_kv_truth(kv->val);
+            else if (strcmp(kv->key, "log") == 0)
+                d->log = install_ini_kv_truth(kv->val);
         }
         break;
     }
@@ -1405,7 +1412,7 @@ static void install_debug_load(install_debug_opts_t *d)
     d->active = d->skip_clean_backup || d->skip_clean_wipe || d->skip_clean_restore
         || d->skip_clean_install || d->skip_clean_staging_cleanup || d->skip_update_cleanup
         || d->skip_update_install || d->skip_update_staging_cleanup || d->skip_update_horizon_oc
-        || d->skip_hekate_8gb_post_copy;
+        || d->skip_hekate_8gb_post_copy || d->log;
 }
 
 static void install_debug_print_banner(const install_debug_opts_t *d)
@@ -1435,17 +1442,39 @@ static void install_debug_print_banner(const install_debug_opts_t *d)
         gfx_printf("  ueberspringe: HorizonOC Update (Backup/Restore)\n");
     if (d->skip_hekate_8gb_post_copy)
         gfx_printf("  ueberspringe: extras RAM / Hekate-Auswahl / Post-Copy\n");
+    if (d->log)
+        gfx_printf("  Log: %s\n", INSTALL_LOG_PATH);
     install_set_color(COLOR_WHITE);
     gfx_printf("\n");
 }
 
+static int perform_installation_steps(omninx_variant_t pack_variant, install_mode_t mode, const install_debug_opts_t *d);
+
 // Main installation function
 int perform_installation(omninx_variant_t pack_variant, install_mode_t mode) {
-    int res;
     install_debug_opts_t dbg;
     install_debug_load(&dbg);
     install_debug_print_banner(&dbg);
 
+    if (dbg.log) {
+        log_init(INSTALL_LOG_PATH);
+        log_write("Version: %s\nModus: %s\nVariante: %d\n\n", VERSION,
+            mode == INSTALL_MODE_UPDATE ? "Update" : "Clean", (u32)pack_variant);
+    }
+
+    int res = perform_installation_steps(pack_variant, mode, &dbg);
+
+    if (log_is_enabled()) {
+        log_write("\n=== Ende: res=%d (%s) ===\n", (u32)res, fs_error_str(res));
+        log_close();
+    }
+    return res;
+}
+
+static int perform_installation_steps(omninx_variant_t pack_variant, install_mode_t mode, const install_debug_opts_t *d) {
+    int res;
+    const install_debug_opts_t dbg = *d;
+
     if (mode == INSTALL_MODE_UPDATE) {
         if (pack_variant == VARIANT_OC && !dbg.skip_update_horizon_oc) {
             bool had_horizon_cfg = install_path_exists(HORIZON_OC_CONFIG_PATH);