feat(schema): implement D-035 converged tag taxonomy as canonical JSON Schema (#168)

- Add content/_schema/dialogue-line.schema.json — canonical standalone line schema
  with all 6 structural + 3 selection + 2 authoring-only tags and $defs for
  monologue extension (character, trigger, prerequisite)
- Update dialogue-pool.schema.json: add dual_lens and notes authoring-only tags,
  add additionalProperties: false to knowledge_grant
- Update monologue-pool.schema.json: add all 6 structural tags as required fields
  for schema compliance (role=player_character, access=[public], trust=surface are
  constrained constants); add topic, mood, dual_lens, notes
- Enumerate all 14 v0.1 situations and 9 v0.1 topics as allowed enum values per D-035
- Fix Rust sync gap: add Situation::Greeting and Mood::Focused to line_pool.rs
  (D-035 Sprint 8 amendments — were in schema but missing from Rust enums, causing
  content with these values to be silently dropped at runtime)
- Update line_preview.rs situation_str, mood_str match arms and help text for
  new variants; all 25 line_pool tests pass

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

server/src/bin/line_preview.rs

@@ -348,7 +348,7 @@ fn run_dialogue(index: &LinePoolIndex, args: &Args) {
                     "situation",
                     "arrival, shift_start, shift_end, shift_transition, bar_evening, \
                      night_shift, investigation, confrontation, social, alone, \
-                     emergency, routine, observation",
+                     emergency, routine, observation, greeting",
                 )
             })
             .collect()
@@ -596,6 +596,7 @@ fn situation_str(s: &Situation) -> &'static str {
         Situation::Emergency => "emergency",
         Situation::Routine => "routine",
         Situation::Observation => "observation",
+        Situation::Greeting => "greeting",
     }
 }
 
@@ -637,5 +638,6 @@ fn mood_str(m: &Mood) -> &'static str {
         Mood::Conflicted => "conflicted",
         Mood::Concerned => "concerned",
         Mood::Relieved => "relieved",
+        Mood::Focused => "focused",
     }
 }