fix(llm): increase receive_timeout to 120s and allow per-call override

The network insight prompt is large and max_tokens is 1500 — DeepSeek
takes longer than 30s. Also plumb opts[:receive_timeout] through so
workers can tune it.

lib/towerops/llm/deepseek.ex

@@ -14,7 +14,7 @@ defmodule Towerops.LLM.DeepSeek do
 
   @default_base_url "https://api.deepseek.com/v1"
   @default_model "deepseek-v4-pro"
-  @receive_timeout 30_000
+  @receive_timeout 120_000
 
   @impl true
   def complete(messages, opts \\ []) do
@@ -55,7 +55,7 @@ defmodule Towerops.LLM.DeepSeek do
         url: base_url <> "/chat/completions",
         json: body,
         headers: [{"authorization", "Bearer " <> api_key}],
-        receive_timeout: @receive_timeout
+        receive_timeout: opts[:receive_timeout] || @receive_timeout
       )
 
     case Req.request(req_opts) do