Add user bug reporting with admin triage (open/read/resolved)

Turns the /report-bug placeholder into a real form (POST /bug-reports,
optionally attributed to the logged-in user) and adds a "Segnalazioni bug"
section to /admin to view and triage them. A logged-in reporter can also
check their own report's status via GET /bug-reports/mine, since anonymous
submissions have no user to show a history to.

Status is a three-state lifecycle (open -> read -> resolved) rather than a
plain boolean, so an admin can acknowledge a report distinctly from actually
fixing it. The schema went through two migrations because the first one
(add bug_reports table) had already been applied against the running
instance with a `resolved` boolean before the three-state design was
decided, so a follow-up migration backfills it into `status` instead of
rewriting already-applied history.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/db/models.py

@@ -188,6 +188,24 @@ class Withdrawal(Base):
     confirmed_at: Mapped[datetime | None] = mapped_column(default=None)
 
 
+class BugReport(Base):
+    __tablename__ = "bug_reports"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    description: Mapped[str] = mapped_column(Text)
+    contact: Mapped[str | None] = mapped_column(String(256), default=None)
+    # Set when the reporter was logged in at submission time; the report page is
+    # reachable both logged-in and logged-out (like GET /rounds/current), so this
+    # stays nullable rather than requiring auth just to file a report.
+    user_id: Mapped[int | None] = mapped_column(ForeignKey("users.id"), default=None)
+    # open -> read -> resolved, admin-driven (app/api/routes/admin.py). "read" is a
+    # distinct step from "resolved" so a reporter checking their own status (only
+    # possible when logged in — see GET /bug-reports/mine) can tell "an admin has
+    # seen this" apart from "this has actually been fixed".
+    status: Mapped[str] = mapped_column(String(16), default="open")
+    created_at: Mapped[datetime] = mapped_column(default=utcnow)
+
+
 class AuditLog(Base):
     __tablename__ = "audit_log"