fix: workflow inference chain — surface llama-server errors, user-turn-last, bundle-relative prompts

- LlamaCppInferenceProvider: check HTTP status and surface the real error body instead of masking it as a ChatCompletionResponse deserialization failure
- PromptRenderer: render the live conversation layer (L1) last so the user turn is the final message (fixes Qwen 'No user query found' 500 when L3 recall is present)
- TomlWorkflowLoader: resolve stage prompts relative to the workflow file's own dir (bundle), CWD-independent; config-dir fallback for globals
- SessionOrchestrator: hard-fail a stage whose declared prompt can't resolve (was a silent user-less request)
- move healthcheck prompts next to the example workflow (examples/workflows/prompts/)

infrastructure/inference/llama_cpp/src/main/kotlin/com/correx/infrastructure/inference/llama/cpp/LlamaCppInferenceProvider.kt

@@ -21,6 +21,7 @@ import io.ktor.client.request.accept
 import io.ktor.client.request.get
 import io.ktor.client.request.post
 import io.ktor.client.request.setBody
+import io.ktor.client.statement.bodyAsText
 import io.ktor.http.ContentType
 import io.ktor.http.contentType
 import io.ktor.serialization.kotlinx.json.json
@@ -106,11 +107,16 @@ class LlamaCppInferenceProvider(
         val encoded = json.encodeToString(body)
         log.debug("sending request to llm: {}", encoded)
 
-        val response = httpClient.post("$baseUrl/v1/chat/completions") {
+        val httpResponse = httpClient.post("$baseUrl/v1/chat/completions") {
             contentType(ContentType.Application.Json)
             accept(ContentType.Application.Json)
             setBody(encoded)
-        }.body<ChatCompletionResponse>()
+        }
+        if (httpResponse.status.value !in 200..299) {
+            val errorBody = httpResponse.bodyAsText()
+            error("llama-server returned ${httpResponse.status.value} ${httpResponse.status.description}: $errorBody")
+        }
+        val response = httpResponse.body<ChatCompletionResponse>()
 
         log.debug("got response from llm: {}", response)
 
@@ -146,4 +152,4 @@ class LlamaCppInferenceProvider(
     }
 
     override fun capabilities(): Set<CapabilityScore> = descriptor.capabilities
-}
+}