feat(retry): LLM retry-on-failure for orchestrator — never returns empty response

Problem: when LLM returned empty content or network error, the orchestrator
immediately stopped with (no response) — visible to user as blank reply.

Solution — 4-layer retry system:

## Go Gateway (gateway/internal/orchestrator/orchestrator.go)
- Extracted shared runLoop() used by Chat(), ChatWithEvents(), ChatWithEventsAndRetry()
- Added RetryPolicy struct: MaxLLMRetries (default 3), InitialDelay (2s),
  MaxDelay (30s), RetryOnEmpty (true)
- callLLMWithRetry(): wraps every LLM call with exponential back-off:
  * retries on HTTP/network error
  * retries on empty choices array
  * retries when content=="" AND finish_reason!="tool_calls" (soft empty)
  * strips tools on attempt > 1 (avoids repeated tool-format errors)
  * logs each attempt; total attempts = MaxLLMRetries + 1 (default: 4)
- Added ChatWithEventsAndRetry() with onRetry callback for client visibility
- SetRetryPolicy() for runtime override

## Config (gateway/config/config.go)
- New fields: MaxLLMRetries (GATEWAY_MAX_LLM_RETRIES, default 3)
             RetryDelaySecs (GATEWAY_RETRY_DELAY_SECS, default 2)

## main.go — wires retry policy from config into orchestrator

## docker-compose.yml
- GATEWAY_REQUEST_TIMEOUT_SECS: 120 → 300 (accommodates up to 4 retries)
- GATEWAY_MAX_LLM_RETRIES=3, GATEWAY_RETRY_DELAY_SECS=2 env vars

## API (handlers.go)
- StartChatSession goroutine now uses ChatWithEventsAndRetry
- onRetry callback emits "thinking" DB event with content "⟳ Retry N: reason"
  so the client sees retry progress in the console panel

## Frontend (client/src/lib/chatStore.ts + client/src/pages/Chat.tsx)
- ConsoleEntry gains content?: string and new type "retry"
- thinking events with content starting "⟳ Retry" → type=retry (amber)
- Chat ConsolePanel renders retry events in amber with RefreshCw icon
  and shows the retry reason string underneath

client/src/lib/chatStore.ts

@@ -53,7 +53,7 @@ export interface Conversation {
 
 export interface ConsoleEntry {
   id: string;
-  type: "thinking" | "tool_call" | "done" | "error";
+  type: "thinking" | "tool_call" | "done" | "error" | "retry";
   tool?: string;
   args?: any;
   result?: any;
@@ -62,6 +62,8 @@ export interface ConsoleEntry {
   durationMs?: number;
   timestamp: string;
   model?: string;
+  /** For thinking events: extra message text (e.g. retry reason) */
+  content?: string;
 }
 
 type StoreEvent = "update" | "console";
@@ -439,9 +441,16 @@ class ChatStore {
         if (ev.seq > maxSeq) maxSeq = ev.seq;
 
         switch (ev.eventType) {
-          case "thinking":
-            this.addConsoleEntry({ type: "thinking" });
+          case "thinking": {
+            // If content starts with retry prefix, show as retry event
+            const thinkMsg = ev.content || "";
+            if (thinkMsg.startsWith("⟳ Retry")) {
+              this.addConsoleEntry({ type: "retry", content: thinkMsg });
+            } else {
+              this.addConsoleEntry({ type: "thinking", content: thinkMsg || undefined });
+            }
             break;
+          }
 
           case "tool_call": {
             let args: any = {};

client/src/pages/Chat.tsx

@@ -51,6 +51,7 @@ import {
   PanelRightOpen,
   Shell,
   StopCircle,
+  RefreshCw,
 } from "lucide-react";
 
 // ─── useChatStore hook ────────────────────────────────────────────────────────
@@ -295,6 +296,8 @@ function ConsolePanel({ entries }: { entries: ConsoleEntry[] }) {
           animate={{ opacity: 1, x: 0 }}
           className={`rounded p-2 border ${
             e.type === "thinking" ? "bg-cyan-500/10 border-cyan-500/20 text-cyan-400"
+              : e.type === "retry"
+                ? "bg-amber-500/10 border-amber-500/20 text-amber-400"
               : e.type === "tool_call"
                 ? e.success !== false ? "bg-green-500/10 border-green-500/20 text-green-300"
                 : "bg-red-500/10 border-red-500/20 text-red-300"
@@ -304,11 +307,13 @@ function ConsolePanel({ entries }: { entries: ConsoleEntry[] }) {
         >
           <div className="flex items-center gap-1.5 mb-1">
             {e.type === "thinking" && <Loader2 className="w-3 h-3 animate-spin" />}
+            {e.type === "retry" && <RefreshCw className="w-3 h-3 text-amber-400" />}
             {e.type === "tool_call" && <ToolIcon tool={e.tool ?? ""} />}
             {e.type === "done" && <CheckCircle className="w-3 h-3" />}
             {e.type === "error" && <XCircle className="w-3 h-3" />}
             <span className="font-semibold">
               {e.type === "thinking" ? "thinking…"
+                : e.type === "retry" ? "retry"
                 : e.type === "tool_call" ? toolLabel(e.tool ?? "")
                 : e.type === "done" ? `done · ${e.model ?? ""}`
                 : "error"}
@@ -316,6 +321,11 @@ function ConsolePanel({ entries }: { entries: ConsoleEntry[] }) {
             <span className="ml-auto text-[9px] opacity-60">{e.timestamp}</span>
           </div>
 
+          {/* Retry reason or thinking message */}
+          {(e.type === "retry" || e.type === "thinking") && e.content && (
+            <div className="text-[9px] opacity-80 mt-0.5 font-mono break-words">{e.content}</div>
+          )}
+
           {e.type === "tool_call" && e.args && (
             <pre className="text-[9px] opacity-70 overflow-hidden max-h-16 whitespace-pre-wrap">
               {JSON.stringify(e.args, null, 1).slice(0, 200)}