Add collector fields, including market value

Rating, notes, condition, region, purchase price and date, plus a market
value carrying the timestamp and source that make it interpretable.

Condition is load-bearing rather than cosmetic: price feeds quote per
condition, so it selects which quoted price applies to a copy. Market value
records when it was captured and where it came from — a collection total is
only as good as its staleness — and an edit to an unrelated field leaves
that timestamp alone, so a stale price cannot start looking freshly checked.

Two storage decisions worth naming:

  * Money is stored as integer minor units. SQLite has no decimal type and
    EF Core maps decimal to TEXT, which compares lexically: "9.00" sorts
    above "10.00" and SUM is unavailable. A value converter keeps decimals
    in C# while ordering and totalling work. A test pins the ordering.
  * Enums serialise as names. The default is ordinals, which meant the API
    rejected the browser's {"condition":"Cib"} with a 400 while the C# tests
    passed, because they round-tripped ints and never spoke the client's
    dialect. The tests now share the API's serializer options.

Also fixes a data-loss bug in the Python tools. Both built their PUT body
from a hardcoded list of field names, so any column added to the model was
omitted and therefore nulled. Adding collector fields meant the next art or
enrichment run would have erased every rating, note, condition, price and
valuation in the library. Payloads are now built by excluding the handful of
server-owned fields, so new columns carry through by default.

The migration was rehearsed against a copy of the live database before being
applied: 105 rows, descriptions and developers intact.

67 backend tests, 8 frontend.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

backend/src/LudosData.Api/Domain/Game.cs

@@ -47,6 +47,41 @@ public class Game
     public bool Played { get; set; }
     public bool Finished { get; set; }
 
+    // ---- collector fields ------------------------------------------------
+
+    /// <summary>Personal score out of 10. Null means unrated, which is not zero.</summary>
+    [Range(1, 10)]
+    public int? Rating { get; set; }
+
+    /// <summary>
+    /// Free-form personal notes. Kept separate from Description, which is
+    /// derived from an external source and may be overwritten by the enricher.
+    /// </summary>
+    public string? Notes { get; set; }
+
+    public GameCondition Condition { get; set; } = GameCondition.Unspecified;
+    public GameRegion Region { get; set; } = GameRegion.Unspecified;
+
+    /// <summary>What was paid for this copy. A fixed historical fact.</summary>
+    public decimal? PurchasePrice { get; set; }
+
+    public DateOnly? PurchaseDate { get; set; }
+
+    // ---- market value ----------------------------------------------------
+    //
+    // Distinct from PurchasePrice: an estimate of what a copy sells for now,
+    // expected to be refreshed from a price feed. Stored with the moment it was
+    // captured and where it came from, because a figure with neither is not
+    // something you can reason about — a total is only as good as its staleness.
+
+    public decimal? MarketValue { get; set; }
+
+    public DateTimeOffset? MarketValueUpdatedAt { get; set; }
+
+    /// <summary>Provenance, e.g. a price feed's name, or "manual".</summary>
+    [MaxLength(100)]
+    public string? MarketValueSource { get; set; }
+
     /// <summary>
     /// Owning user. Every query is filtered on this server-side, from the JWT subject —
     /// it is never accepted from the client.