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/)

core/inference/src/main/kotlin/com/correx/core/inference/PromptRenderer.kt

@@ -12,6 +12,14 @@ data class ChatMessage(
 )
 
 object PromptRenderer {
+    // L1 (live conversation, ends with the current user turn) must render last so
+    // the model template sees the user query as the final message. Background/memory
+    // layers (L2, L3, L4) are injected before it.
+    private val nonL0RenderOrder: Comparator<ContextLayer> = Comparator { a, b ->
+        val priority = { layer: ContextLayer -> if (layer == ContextLayer.L1) Int.MAX_VALUE else layer.ordinal }
+        priority(a) - priority(b)
+    }
+
     fun render(contextPack: ContextPack): List<ChatMessage> {
         val sorted = contextPack.layers.entries.sortedBy { it.key.ordinal }
         val systemContent = sorted
@@ -19,19 +27,22 @@ object PromptRenderer {
             .flatMap { it.value }
             .joinToString("\n\n") { it.content }
             .takeIf { it.isNotBlank() }
-        val conversationMessages = sorted.filter { it.key != ContextLayer.L0 }.flatMap { (_, entries) ->
-            entries.map { entry ->
-                ChatMessage(
-                    role = when (entry.role) {
-                        EntryRole.SYSTEM -> "system"
-                        EntryRole.ASSISTANT -> "assistant"
-                        EntryRole.TOOL -> "tool"
-                        EntryRole.USER -> "user"
-                    },
-                    content = entry.content,
-                )
+        val conversationMessages = contextPack.layers.entries
+            .filter { it.key != ContextLayer.L0 }
+            .sortedWith(Comparator.comparing({ it.key }, nonL0RenderOrder))
+            .flatMap { (_, entries) ->
+                entries.map { entry ->
+                    ChatMessage(
+                        role = when (entry.role) {
+                            EntryRole.SYSTEM -> "system"
+                            EntryRole.ASSISTANT -> "assistant"
+                            EntryRole.TOOL -> "tool"
+                            EntryRole.USER -> "user"
+                        },
+                        content = entry.content,
+                    )
+                }
             }
-        }
         val messages = buildList {
             systemContent?.let { add(ChatMessage("system", it)) }
             addAll(conversationMessages)