fix: zero-pad date fallback so SQLite ORDER BY date works correctly

The API fallback f"{year}-{month}-{day}" used unpadded keys, producing
dates like "2026-3-2" that break lexicographic sorting (June sorts
before March, 11 before 2).  Now zero-pads via :02d formatting.
Also simplified sync_dates_from_sub to catch all mismatches including
legacy unpadded dates.

Author: LeafCreeper

src/api/icourse.py

@@ -149,9 +149,10 @@ def get_course_detail(self, course_id: str) -> dict:
                             # Real lecture date is embedded in sub_title
                             # ("2026-03-05第6-8节" → "2026-03-05"); fall back
                             # to the server's year/month/day keys if missing.
+                            # Zero-pad the fallback so SQLite ORDER BY works.
                             date = (
                                 _extract_date_from_sub(sub_title)
-                                or f"{year}-{month}-{day}"
+                                or f"{int(year):04d}-{int(month):02d}-{int(day):02d}"
                             )
                             lectures.append(
                                 {

src/data/database.py

@@ -400,16 +400,18 @@ def get_unsent_lectures(self) -> list[dict]:
         return [dict(row) for row in rows]
 
     def sync_dates_from_sub(self) -> int:
-        """Fix existing date rows where sub_title date differs from date column.
+        """Fix date rows where the stored value is wrong or badly formatted.
 
         sub_title format is "2026-03-05第6-8节"; the embedded date is the
-        real class date. Returns number of rows corrected.
+        real class date.  Also corrects zero-padding so that SQLite ORDER BY
+        date works correctly (e.g. "2026-3-2" → "2026-03-02").
+        Returns number of rows corrected.
         """
         with self.conn:
             cur = self.conn.execute(r"""
                 UPDATE lectures
                 SET date = substr(sub_title, 1, 10)
                 WHERE sub_title GLOB '????-??-??*'
-                  AND substr(sub_title, 1, 10) != date
+                  AND date != substr(sub_title, 1, 10)
             """)
             return cur.rowcount or 0