fix: multi-model routing — each adapter uses own dspy.LM instance

- DSPyLLMAdapter now accepts dspy.LM instead of model string, uses dspy.context(lm=...)
- DSPyJudgeAdapter, DSPyProposerAdapter, DSPySyntheticAdapter each accept and use own LM
- OptimizationConfig gains per-model api_base/api_key_env override fields
- cli/app.py creates separate dspy.LM per adapter with per-model overrides
- New unit tests verify each adapter isolates its LM from global config

Fixes Bug #1 (multi-model config not wired) and Bug #2 (DSPyLLMAdapter ignores model param).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/prometheus/infrastructure/proposer_adapter.py

@@ -6,6 +6,8 @@ Converts trajectories into readable format for the LLM proposer.
 """
 from __future__ import annotations
 
+import dspy
+
 from prometheus.domain.entities import Prompt, Trajectory
 from prometheus.domain.ports import ProposerPort
 from prometheus.infrastructure.dspy_modules import InstructionProposer
@@ -14,7 +16,8 @@ from prometheus.infrastructure.dspy_modules import InstructionProposer
 class DSPyProposerAdapter(ProposerPort):
     """Uses evaluation trajectories to build a failure report and propose a new prompt."""
 
-    def __init__(self) -> None:
+    def __init__(self, lm: dspy.LM) -> None:
+        self._lm = lm
         self._proposer = InstructionProposer()
 
     def propose(
@@ -24,11 +27,12 @@ class DSPyProposerAdapter(ProposerPort):
         task_description: str,
     ) -> Prompt:
         failure_examples = self._format_failures(trajectories)
-        pred = self._proposer(
-            current_instruction=current_prompt.text,
-            task_description=task_description,
-            failure_examples=failure_examples,
-        )
+        with dspy.context(lm=self._lm):
+            pred = self._proposer(
+                current_instruction=current_prompt.text,
+                task_description=task_description,
+                failure_examples=failure_examples,
+            )
         return Prompt(text=pred.new_instruction)
 
     @staticmethod