v4.1: BiliBili Live filename auto-rename

- Add a '✨ Rename' button and live preview to the Output Settings section
- Convert BiliBili Live recording stems of the form
  '[YYYY-MM-DD HH-MM-SS][streamer][title]' into
  'YYYY年MM月DD日【直播回放】title'
- Preview shows the converted result and enables/disables the button based
  on whether the current name matches the pattern
- On auto-fill, keep the raw stem (no '_concat' suffix) so the pattern can
  match; strip a trailing '_concat' before matching as well

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

video_concat.py

@@ -316,7 +316,7 @@ class App(_BaseClass):  # type: ignore[valid-type]
 
         # Name row
         r1 = ctk.CTkFrame(body, fg_color="transparent")
-        r1.pack(fill="x", pady=(0, 8))
+        r1.pack(fill="x", pady=(0, 4))
         ctk.CTkLabel(r1, text="File name:", width=96, anchor="w").pack(side="left")
         ctk.CTkEntry(r1, textvariable=self.out_name_var).pack(side="left", fill="x", expand=True)
         ctk.CTkOptionMenu(
@@ -324,6 +324,24 @@ class App(_BaseClass):  # type: ignore[valid-type]
             variable=self.out_ext_var, width=84
         ).pack(side="left", padx=(8, 0))
 
+        # Auto-rename button — converts BiliBili Live filename to readable format
+        self.rename_btn = ctk.CTkButton(
+            r1, text="✨ Rename", width=110,
+            fg_color=("#EDE9FE", "#3B1F6E"),
+            text_color=("#5B21B6", "#C4B5FD"),
+            hover_color=("#DDD6FE", "#4C2889"),
+            command=self._apply_bililive_rename
+        )
+        self.rename_btn.pack(side="left", padx=(8, 0))
+
+        # Preview label: shows what the rename will produce before applying
+        self.rename_preview_lbl = ctk.CTkLabel(
+            body, text="",
+            font=ctk.CTkFont(size=11), text_color=("#7C3AED", "#A78BFA"),
+            anchor="w"
+        )
+        self.rename_preview_lbl.pack(fill="x", pady=(0, 4))
+
         # Directory row
         r2 = ctk.CTkFrame(body, fg_color="transparent")
         r2.pack(fill="x")
@@ -504,8 +522,61 @@ class App(_BaseClass):  # type: ignore[valid-type]
         self.out_path_lbl.configure(
             text=f"Output path:  {out}" if out else "Output path: —"
         )
+        self._refresh_rename_preview()
         self._refresh_start()
 
+    def _refresh_rename_preview(self):
+        """Show a live preview of what the rename button will produce."""
+        if not hasattr(self, "rename_preview_lbl"):
+            return
+        current = self.out_name_var.get().strip()
+        renamed = self._bililive_rename(current)
+        if renamed and renamed != current:
+            self.rename_preview_lbl.configure(
+                text=f"  → {renamed}"
+            )
+            self.rename_btn.configure(state="normal")
+        else:
+            self.rename_preview_lbl.configure(text="")
+            # Only disable if the name cannot be converted
+            self.rename_btn.configure(state="disabled" if not renamed else "normal")
+
+
+    # ══════════════════════════════════════════════════════════════════════════
+    #  BiliBili Live filename auto-rename
+    # ══════════════════════════════════════════════════════════════════════════
+
+    # Pattern: [2025-06-28 20-31-15][纳豆nado][title content]
+    _BILILIVE_RE = re.compile(
+        r"^\[(\d{4})-(\d{2})-(\d{2}) \d{2}-\d{2}-\d{2}\]\[[^\]]*\]\[(.+)\]$"
+    )
+
+    @staticmethod
+    def _bililive_rename(stem: str) -> str:
+        """
+        Convert a BiliBili Live recording stem to a readable name.
+        Input:  [2026-03-14 22-46-37][纳豆nado][【点歌专场】今晚九点来捏]
+        Output: 2026年03月14日【直播回放】【点歌专场】今晚九点来捏
+        Returns the converted string, or "" if the stem does not match.
+        """
+        # Strip any trailing _concat suffix before matching
+        test = stem.removesuffix("_concat").strip()
+        m = App._BILILIVE_RE.match(test)
+        if not m:
+            return ""
+        year, month, day, title = m.groups()
+        return f"{year}年{month}月{day}日【直播回放】{title}"
+
+    def _apply_bililive_rename(self):
+        """Apply the rename conversion to the current output name."""
+        current = self.out_name_var.get().strip()
+        renamed = self._bililive_rename(current)
+        if not renamed:
+            return
+        self.out_name_var.set(renamed)
+        self.rename_preview_lbl.configure(text="  ✓ Renamed!")
+        self.rename_btn.configure(state="disabled")
+
     def _refresh_start(self):
         if not hasattr(self, "start_btn"):
             return   # UI not fully built yet
@@ -572,7 +643,8 @@ class App(_BaseClass):  # type: ignore[valid-type]
         if not self.out_dir_var.get().strip():
             self.out_dir_var.set(str(Path(self.items[0]["path"]).parent))
         if self.out_name_var.get() in ("", "output_concat"):
-            self.out_name_var.set(Path(self.items[0]["path"]).stem + "_concat")
+            # Keep the raw BiliBili stem so the rename pattern can match it
+            self.out_name_var.set(Path(self.items[0]["path"]).stem)
 
         self._rebuild_list()
         self._update_count()