Add viewer database import and clarify backup actions.

Pairs export with validated .db restore, documents the difference from game
save imports, and renames the JSON upload button to Import game backup.

Co-authored-by: Cursor <cursoragent@cursor.com>

viewers.py

@@ -2,14 +2,24 @@
 
 from __future__ import annotations
 
+import os
 import re
 import secrets
+import shutil
+import sqlite3
 from pathlib import Path
 
 from db import get_connection, init_db
 
 VIEWER_ID_RE = re.compile(r"^[A-Za-z0-9_-]{16,64}$")
 LOCAL_VIEWER_ID = "local"
+VIEWER_DB_TABLES = frozenset({
+    "snapshots",
+    "inventory_snapshots",
+    "skill_snapshots",
+    "goals",
+    "goal_groups",
+})
 
 
 def generate_viewer_id() -> str:
@@ -79,3 +89,49 @@ def get_or_create_cli_viewer(data_dir: Path) -> str:
     viewer_id = create_viewer(data_dir)
     marker.write_text(viewer_id, encoding="utf-8")
     return viewer_id
+
+
+def inspect_viewer_db(db_path: Path) -> dict[str, int]:
+    """Validate a viewer SQLite file and apply schema migrations."""
+    if not db_path.is_file():
+        raise ValueError("Database file not found")
+    try:
+        conn = get_connection(db_path)
+    except sqlite3.DatabaseError as exc:
+        raise ValueError("Not a valid SQLite database") from exc
+    try:
+        tables = {
+            row[0]
+            for row in conn.execute(
+                "SELECT name FROM sqlite_master WHERE type='table'"
+            )
+        }
+        missing = VIEWER_DB_TABLES - tables
+        if missing:
+            raise ValueError("Not a valid Idle Fantasy viewer database")
+        init_db(conn)
+        conn.commit()
+        snapshots = conn.execute("SELECT COUNT(*) AS c FROM snapshots").fetchone()["c"]
+        goals = conn.execute("SELECT COUNT(*) AS c FROM goals").fetchone()["c"]
+        goal_groups = conn.execute("SELECT COUNT(*) AS c FROM goal_groups").fetchone()["c"]
+        return {
+            "snapshots": snapshots,
+            "goals": goals,
+            "goal_groups": goal_groups,
+        }
+    finally:
+        conn.close()
+
+
+def restore_viewer_db(source: Path, target: Path) -> dict[str, int]:
+    """Replace a viewer database with a validated copy."""
+    stats = inspect_viewer_db(source)
+    target.parent.mkdir(parents=True, exist_ok=True)
+    staging = target.with_suffix(".db.importing")
+    shutil.copy2(source, staging)
+    try:
+        os.replace(staging, target)
+    except OSError:
+        staging.unlink(missing_ok=True)
+        raise
+    return stats