feat(serving): replace MLflow run logging with native trace spans

Convert ml-serving from isolated MLflow runs to nested traces using
mlflow.start_span_no_context(). The recommend endpoint now emits a full
span tree: recommend (CHAIN) → build_context (TOOL), agent:* (AGENT) ×N,
llm_orchestrator (LLM). Compute and infer endpoints each emit a single span.

Supporting changes:
- mlflow-skinny>=3.1.0 added to requirements
- MLflow configured with --serve-artifacts + mlflow-artifacts:/ default root
  for cross-container artifact proxy (spans now persist from ml-serving)
- --allowed-hosts extended to include mlflow:5000 (SDK includes port in Host)
- science_destiny slider wired through prompts.py and recommend endpoint
- Config page exposes science/destiny slider (0=data-driven, 100=intuitive)
- Tip page shows rationale inline on tap

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

ml/serving/prompts.py

@@ -124,17 +124,52 @@ _SYS_V4_ORCHESTRATOR = (
 )
 
 
+def _science_destiny_instruction(science_destiny: int) -> str:
+    """Translate 0-100 slider into a prompt instruction.
+
+    0   = pure science: prioritise patterns, data, measurable progress.
+    100 = pure destiny: prioritise meaning, intuition, deeper purpose.
+    50  = balanced (no extra instruction injected).
+    """
+    if science_destiny <= 20:
+        return (
+            "The user strongly prefers data-driven advice. "
+            "Ground every tip in observable patterns, streaks, or measurable progress. "
+            "Avoid abstract or motivational language."
+        )
+    if science_destiny <= 40:
+        return (
+            "The user leans toward evidence-based guidance. "
+            "Anchor tips in patterns and metrics where possible."
+        )
+    if science_destiny >= 80:
+        return (
+            "The user strongly believes in intuition and meaning. "
+            "Frame tips around purpose, values, and deeper intention rather than metrics."
+        )
+    if science_destiny >= 60:
+        return (
+            "The user leans toward intuitive, meaning-driven advice. "
+            "Weave in purpose and intention alongside practicality."
+        )
+    return ""  # balanced — no extra instruction
+
+
 def build_orchestrator_messages(
     agent_outputs: list[dict],
     tasks: list[dict],
     hour_of_day: int,
     day_of_week: int,
+    science_destiny: int = 50,
 ) -> list[dict]:
     """Build the [system, user] message list for the orchestrator LLM call.
 
     agent_outputs: list of {agent_id, prompt_text} dicts.
     Falls back to raw task summary when agent_outputs is empty.
     """
+    style_hint = _science_destiny_instruction(science_destiny)
+    system = _SYS_V4_ORCHESTRATOR + (f"\n\n{style_hint}" if style_hint else "")
+
     lines = [f"Current time: {hour_of_day:02d}:00, day_of_week={day_of_week}", ""]
     if agent_outputs:
         lines.append("Context from analysis agents:")
@@ -150,7 +185,7 @@ def build_orchestrator_messages(
             lines.append(f"  - {t.get('content', '?')}")
     lines.append("\nGenerate one tip as a JSON object. Write the tip content in English only.")
     return [
-        {"role": "system", "content": _SYS_V4_ORCHESTRATOR},
+        {"role": "system", "content": system},
         {"role": "user", "content": "\n".join(lines)},
     ]