fix(portfolio-master): visible skip warning + clearer caption

When a user selects a folder in the upload picker (browser behaviour
that bypasses type filter), all files come through and only valid
extensions get processed. Make the skipped count visible and update
the caption to set expectations.

view_portfolio_master.py

@@ -544,7 +544,8 @@ def render():
     # ── Upload ───────────────────────────────────────────────────────────────
     with st.expander("📂  Upload Backtest Files",
                      expanded=not bool(st.session_state.pm_files)):
-        st.caption("Accepts `.htm` · `.html` · `.csv`")
+        st.caption("Accepts `.htm` · `.html` · `.csv` — selecting a folder will only "
+                   "import the supported files inside it (others are skipped).")
         uploaded = st.file_uploader(
             "Select files",
             type=["htm", "html", "csv"],
@@ -552,9 +553,15 @@ def render():
             key=f"pm_uploader_{st.session_state.pm_uploader_key}",
         )
         if uploaded:
-            # Streamlit already filters by type, defensive check anyway
-            uploaded = [f for f in uploaded
+            # Some browsers ignore the type filter when a folder is selected —
+            # filter again here and report what was skipped.
+            valid    = [f for f in uploaded
                         if f.name.lower().endswith((".htm",".html",".csv"))]
+            rejected = len(uploaded) - len(valid)
+            if rejected:
+                st.warning(f"⚠️ Skipped {rejected} non-supported file(s). "
+                           f"Importing {len(valid)} valid file(s).")
+            uploaded = valid
             for f in uploaded:
                 stem = os.path.splitext(f.name)[0]
                 if stem not in st.session_state.pm_files: