debug: log every product_edit view hit + use /opt path for log

The /tmp/mps-pricing-debug.log file didn't appear after fox triggered
a save attempt. Two changes to narrow down why:

1. Move the debug log to /opt/make_post_sell/pricing-debug.log (where
   uwsgi has owner write access) with /tmp as fallback. PrivateTmp or
   permissions might be blocking /tmp writes on this systemd setup.

2. Add an ENTER log line at the top of product_edit() that fires for
   every request — GET, POST, save, etc. If this line never appears,
   the view itself isn't being reached and the form is going somewhere
   else. If it appears but the pricing_mode line doesn't, the submit
   field is missing from params.

make_post_sell/views/product.py

@@ -255,6 +255,30 @@ def product_edit(request):
     product_modified = False
     product = request.product
 
+    # TEMPORARY DEBUG: log every product_edit hit so we can confirm the
+    # view is even being reached when fox attempts to save pricing_mode.
+    import os as _os_dbg
+    import time as _time_dbg
+    for _path_dbg in (
+        "/opt/make_post_sell/pricing-debug.log",
+        "/tmp/mps-pricing-debug.log",
+    ):
+        try:
+            with open(_path_dbg, "a") as _f_dbg:
+                _f_dbg.write(
+                    f"{_time_dbg.time():.3f} pid={_os_dbg.getpid()} ENTER product_edit "
+                    f"product={product.uuid_str} method={request.method} "
+                    f"submit={'submit' in request.params} "
+                    f"pricing_mode={request.params.get('pricing_mode')!r}\n"
+                )
+            try:
+                _os_dbg.chmod(_path_dbg, 0o644)
+            except Exception:
+                pass
+            break
+        except Exception:
+            continue
+
     title = request.params.get("title", product.title).strip()
     description = request.params.get("description", product.description).strip()
     price = request.params.get("price", product.price)
@@ -330,19 +354,33 @@ def product_edit(request):
             )
         except Exception:
             pass
-        try:
-            import time as _time
-            with open("/tmp/mps-pricing-debug.log", "a") as _f:
-                _f.write(
-                    f"{_time.time():.3f} product={product.uuid_str} "
-                    f"current={product.pricing_mode} "
-                    f"pricing_mode={request.params.get('pricing_mode')!r} "
-                    f"all_modes={list(request.params.getall('pricing_mode')) if hasattr(request.params, 'getall') else 'no-getall'} "
-                    f"submit={request.params.get('submit')!r} "
-                    f"all_keys={sorted(request.params.keys())}\n"
-                )
-        except Exception:
-            pass
+        # Write to a path under /opt/make_post_sell where uwsgi has
+        # write access; /tmp may be sandboxed under PrivateTmp on some
+        # systemd configurations. World-readable so fox can tail without sudo.
+        import os as _os
+        import time as _time
+        for _path in (
+            "/opt/make_post_sell/pricing-debug.log",
+            "/tmp/mps-pricing-debug.log",
+        ):
+            try:
+                with open(_path, "a") as _f:
+                    _f.write(
+                        f"{_time.time():.3f} pid={_os.getpid()} "
+                        f"product={product.uuid_str} "
+                        f"current={product.pricing_mode} "
+                        f"pricing_mode={request.params.get('pricing_mode')!r} "
+                        f"all_modes={list(request.params.getall('pricing_mode')) if hasattr(request.params, 'getall') else 'no-getall'} "
+                        f"submit={request.params.get('submit')!r} "
+                        f"all_keys={sorted(request.params.keys())}\n"
+                    )
+                try:
+                    _os.chmod(_path, 0o644)
+                except Exception:
+                    pass
+                break
+            except Exception:
+                continue
         try:
             new_mode = int(request.params.get("pricing_mode", product.pricing_mode))
         except (TypeError, ValueError):