Tracing: LLM clients + streaming spans on tracing, drop cx threading (#140)

LlmClient methods no longer take an OpenTelemetry Context. llm.request is
now a tracing span (otel.kind=client, llm.provider/operation/model) that
parents on the caller's ambient span; traceparent injection reads the
span's OTel context via OpenTelemetrySpanExt.

The src/ai feature spans (handlers, insight generation, chat, persona
chat, daily summaries, TTS) move to #[instrument] / info_span!, and every
LLM-bearing tokio::spawn carries its parent span with .instrument(): the
streaming chat turn (chat_turn_stream_inner), async chat / persona turns,
background insight jobs and TTS jobs. Sub-spans in the agentic loops
(ai.chat.loop, ai.agentic.loop) instrument each LLM / tool await.

DAO calls keep their explicit Context (derived from the tracing span)
until the DAO migration (#141).

tests/otel_llm_spans.rs pins nesting + traceparent for the blocking and
streaming paths across a spawn on a multi-thread runtime.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/ai/sms_client.rs

@@ -324,7 +324,6 @@ impl SmsApiClient {
         &self,
         messages: &[SmsMessage],
         ollama: &OllamaClient,
-        cx: &opentelemetry::Context,
     ) -> Result<String> {
         if messages.is_empty() {
             return Ok(String::from("No messages on this day"));
@@ -357,7 +356,6 @@ Summary:"#,
 
         ollama
             .generate(
-                cx,
                 &prompt,
                 // Some("You are a summarizer for the purposes of jogging my memory and highlighting events and situations."),
                 Some("You are the keeper of memories, ingest the context and give me a casual summary of the moment."),