fix: display db timestamps in Brussels time

(heure de dépôt was showing UTC)

- feat: add date_depot column (real TFE deposit date)
with CSV round-trip + Brussels→UTC sanitization
- fix: keep PHP default tz at UTC to preserve token/share-link
 expiry consistency; convert to Brussels only in db_datetime()

app/storage/schema.sql

@@ -99,6 +99,7 @@ CREATE TABLE IF NOT EXISTS theses (
     jury_points DECIMAL(4,2),
     jury_note_added BOOLEAN DEFAULT 0,
     submitted_at DATETIME,
+    date_depot DATETIME, -- real TFE deposit date (bulk-import source, Brussels-local parse → UTC storage)
     defense_date DATETIME,
     published_at DATETIME,
     is_published BOOLEAN DEFAULT 0,
@@ -447,6 +448,7 @@ SELECT
     t.access_type_id,
     t.jury_points,
     t.submitted_at,
+    t.date_depot,
     t.defense_date,
     t.published_at,
     t.is_published,