refactor(agent): extract agent+shared into standalone packages with full GRACE semantic markup

- Move agent code from backend/src/agent/ to agent/src/ss_tools/agent/
- Extract shared stdlib-only utilities to shared/src/ss_tools/shared/
- Add #region/#endregion contracts to all ~140 functions (INV_1 compliance)
- Update docker files, entrypoint, build scripts for new package layout
- Backend now imports ss_tools.shared._llm_health (no gradio/langchain deps)
- Add specs for 036-039 feature plans

agent/src/ss_tools/agent/_llm_params.py

@@ -0,0 +1,75 @@
+# agent/src/ss_tools/agent/_llm_params.py
+# #region AgentChat.LlmParams [C:3] [TYPE Module] [SEMANTICS agent-chat,llm,openai,compatibility]
+# @BRIEF Build provider-safe ChatOpenAI kwargs and raw OpenAI payloads.
+# @POST Unsupported sampling parameters are omitted for reasoning/codex models.
+from typing import Any
+
+_TEMPERATURE_UNSUPPORTED_PREFIXES = (
+    "codex/",
+    "omni/codex/",
+    "gpt-5",
+    "o1",
+    "o3",
+    "o4",
+)
+
+
+# #region AgentChat.LlmParams.CanonicalModelName [C:1] [TYPE Function] [SEMANTICS agent-chat,llm,model,canonical]
+# @ingroup AgentChat
+# @BRIEF Strip provider prefix from model name for compatibility checks.
+def _canonical_model_name(model: str | None) -> str:
+    name = (model or "").strip().lower()
+    if name.startswith(("codex/", "omni/codex/")):
+        return name
+    if "/" in name:
+        return name.rsplit("/", 1)[-1]
+    return name
+# #endregion AgentChat.LlmParams.CanonicalModelName
+
+
+# #region AgentChat.LlmParams.SupportsTemperature [C:1] [TYPE Function] [SEMANTICS agent-chat,llm,temperature,check]
+# @ingroup AgentChat
+# @BRIEF Check if a model supports temperature parameter (reasoning/codex models don't).
+def supports_temperature(model: str | None) -> bool:
+    name = _canonical_model_name(model)
+    return not any(name.startswith(prefix) for prefix in _TEMPERATURE_UNSUPPORTED_PREFIXES)
+# #endregion AgentChat.LlmParams.SupportsTemperature
+
+
+# #region AgentChat.LlmParams.ChatOpenAIKwargs [C:2] [TYPE Function] [SEMANTICS agent-chat,llm,openai,kwargs]
+# @ingroup AgentChat
+# @BRIEF Build ChatOpenAI constructor kwargs with provider-safe parameters.
+def chat_openai_kwargs(
+    *,
+    model: str,
+    base_url: str | None,
+    api_key: str,
+    max_tokens: int,
+    temperature: float = 0,
+) -> dict[str, Any]:
+    kwargs: dict[str, Any] = {
+        "model": model,
+        "base_url": base_url,
+        "api_key": api_key,
+        "max_tokens": max_tokens,
+    }
+    if supports_temperature(model):
+        kwargs["temperature"] = temperature
+    return kwargs
+# #endregion AgentChat.LlmParams.ChatOpenAIKwargs
+
+
+# #region AgentChat.LlmParams.AddTemperature [C:2] [TYPE Function] [SEMANTICS agent-chat,llm,payload,temperature]
+# @ingroup AgentChat
+# @BRIEF Conditionally add temperature to raw OpenAI payload dict.
+def add_temperature_if_supported(
+    payload: dict[str, Any],
+    *,
+    model: str | None,
+    temperature: float = 0,
+) -> dict[str, Any]:
+    if supports_temperature(model):
+        payload["temperature"] = temperature
+    return payload
+# #endregion AgentChat.LlmParams.AddTemperature
+# #endregion AgentChat.LlmParams