JR-004, JR-005, JR-006: scene-scoped read path

Presence was decided by a LINQ predicate inline in the controller, so the
semantics SR-002 sets were nowhere stated in code -- the read path complied by
accident rather than by requirement. PresenceLookup is now the unit that
decides, tagged, with the reasoning next to it.

JR-004: windows are served exactly as given. UT-021 pins that [0,10] and
[10,20] are not merged despite looking mergeable -- two windows mean a genuine
departure and return, and collapsing them answers a different question from the
one the truth file asked. UT-022 pins a byte-identical round trip.

JR-005: bounds inclusive at both ends, zero-length windows are real sightings
rather than degenerate ones to discard, overlaps resolve.

The wording was the larger half of JR-005. The overlay rendered a bare list: it
asserted nothing, but told the viewer nothing either, and the default reading of
a paused frame is "these people are on screen" -- exactly what SR-002 forbids.
It now carries an "In this scene" heading. ActorAtTime became ActorInScene, and
README no longer contains "on screen" anywhere; it stated the forbidden reading
outright in seven places, including the opening sentence.

JR-006: measured rather than assumed. UT-023 builds 50 actors x 1000 windows and
asserts the response is bounded by actor count, never window count. The lookup
is a full scan on purpose -- an early exit on `start > t` would exploit the
sortedness the format requires, but would silently under-report the moment one
producer emitted windows out of order. UT-020 pins that unsorted input still
resolves; WindowsAreSorted is a diagnostic, not a correctness dependency.

Third mutation check: making the end bound exclusive fails UT-016 and UT-018 and
nothing else. One character turns an inclusive window into a half-open one,
dropping an actor at exactly the moment a scene ends.

TRACES: UT-016, UT-017, UT-018, UT-019, UT-020, UT-021, UT-022, UT-023
TRACES: JR-004, JR-005, JR-006 | SR-002

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

Jellyfin.Plugin.JRay/Models/ActorInScene.cs

@@ -0,0 +1,41 @@
+using System.Text.Json.Serialization;
+
+namespace Jellyfin.Plugin.JRay.Models;
+
+/// <summary>
+/// An actor present in the scene at a queried timestamp.
+/// </summary>
+/// <remarks>
+/// "Present in the scene", not "visible on screen". The truth file makes a claim
+/// about scene membership, so an actor who has turned away or is off-camera
+/// during a reverse shot is still present. The type was named
+/// <c>ActorAtTime</c>, which invited exactly the instantaneous reading SR-002
+/// forbids.
+/// </remarks>
+// TRACES: JR-005 | SR-002
+public class ActorInScene
+{
+    /// <summary>
+    /// Gets or sets the actor's display name.
+    /// </summary>
+    [JsonPropertyName("name")]
+    public string Name { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Gets or sets the actor's IMDB person id, or "" if unresolved.
+    /// </summary>
+    [JsonPropertyName("imdb_id")]
+    public string ImdbId { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Gets or sets the actor's TMDB person id, or "" if unresolved.
+    /// </summary>
+    [JsonPropertyName("tmdb_id")]
+    public string TmdbId { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Gets or sets the actor's Jellyfin Person item GUID, or "" if unresolved.
+    /// </summary>
+    [JsonPropertyName("jellyfin_id")]
+    public string JellyfinId { get; set; } = string.Empty;
+}