feat(simulation): NPC mood state machine (#323, D-024, D-035)

8-state NPC mood FSM driven by stress, time of day, and interaction events.
Adds MoodState component, derive_mood() pure function, and update_mood() Bevy
system wired into NpcPlugin. Adds Focused as 9th Mood content tag (D-035
Sprint 8 amendment). Syncs CurrentMood for Layer 4 dialogue selection.

31 unit tests covering priority ordering, boundary conditions, and system
integration. All random values route through SimRng (D-010 determinism).
No floats. No HashMap.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/src/content/line_pool.rs

@@ -157,6 +157,7 @@ impl FromStr for Topic {
 }
 
 /// D-028 Layer 4: Mood tag — influences weighted selection.
+/// D-035 amendment (Sprint 8): `Focused` added as 9th variant.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub enum Mood {
     Fond,
@@ -167,6 +168,9 @@ pub enum Mood {
     Conflicted,
     Concerned,
     Relieved,
+    /// D-035 amendment (Sprint 8): task-focused NPC mood — used at The Terminal
+    /// and maintenance corridors. Maps from NpcMood::Focused.
+    Focused,
 }
 
 impl FromStr for Mood {
@@ -181,6 +185,7 @@ impl FromStr for Mood {
             "conflicted" => Ok(Self::Conflicted),
             "concerned" => Ok(Self::Concerned),
             "relieved" => Ok(Self::Relieved),
+            "focused" => Ok(Self::Focused),
             _ => Err(ParseEnumError {
                 kind: "Mood",
                 value: s.to_string(),