feat(inference): operator-tunable sampling knobs (top_k/min_p/repeat_penalty) for stage requests

GenerationConfig only carried temperature/top_p/max_tokens/stop/seed. Added nullable
topK/minP/repeatPenalty, serialized to the llama.cpp and OpenAI-compat request bodies
via @EncodeDefault(NEVER) so an unset knob is omitted (the model keeps its own default)
and behavior is unchanged unless the operator opts in.

Surfaced as a new [sampling] config section feeding the default stage GenerationConfig
(the main agentic loop) through TomlWorkflowLoader + ExecutionPlanCompiler; the former
hardcoded temperature=0.7/topP=1.0 stage defaults now come from config. Talkie
chat/narration keep their own generation settings.

Vikunja #46 (task 76) — sampling half.

apps/server/src/main/kotlin/com/correx/apps/server/Main.kt

@@ -385,10 +385,23 @@ fun main() {
     // Plan-compile gate: wrap the ExecutionPlanCompiler as a post-stage check so a compile-invalid
     // architect plan is handed back through the retry-feedback loop instead of parking the session in
     // ACTIVE (post-planning compile dead-end). Returns null on success, the compiler message on failure.
+    // Operator sampling defaults ([sampling] config) sent on every stage inference request. maxTokens=0
+    // is a placeholder; the loader/compiler pin it per-stage to the token budget via copy().
+    val stageSamplingDefaults = with(correxConfig.sampling) {
+        GenerationConfig(
+            temperature = temperature,
+            topP = topP,
+            maxTokens = 0,
+            topK = topK,
+            minP = minP,
+            repeatPenalty = repeatPenalty,
+        )
+    }
     val planCompiler = ExecutionPlanCompiler(
         artifactKindRegistry,
         toolRegistry.all().map { it.name }.toSet(),
         injectRecovery = true,
+        samplingDefaults = stageSamplingDefaults,
     )
     // Startup-load orchestration tuning from the [orchestration] config section into the kernel's
     // OrchestrationTuning. ponytail: read once at boot — a config edit needs a restart to take effect
@@ -449,7 +462,7 @@ fun main() {
         tuning = orchestrationTuning,
     )
     val workflowRegistry = FileSystemWorkflowRegistry(
-        InfrastructureModule.createWorkflowLoader(configArtifactKindsEarly),
+        InfrastructureModule.createWorkflowLoader(configArtifactKindsEarly, stageSamplingDefaults),
     )
     // Builds the router facade from a config snapshot, mapping the [router] block onto the domain
     // TalkieConfig. Reused by ConfigService's rebuild hook so router knob edits apply live (the