fix: agentic loop robustness — tool arg sanitisation, geocoding, better errors

- Sanitise tool call arguments before re-sending in conversation history: non-object values (bool, string, null) that some models produce are normalised to {} to prevent Ollama 500s
- Map 'error parsing tool call' Ollama 500 to HTTP 400 with a descriptive message listing compatible models (llama3.1, llama3.2, qwen2.5, mistral-nemo)
- Add reverse_geocode tool backed by existing Nominatim helper; description hints model can chain it after get_location_history results
- Make get_sms_messages contact parameter optional (was required, forcing the model to guess); executor now passes None to fall back to all-contacts search
- Log tool result outcomes at warn level for errors/empty results, info for successes; log SMS API errors with full detail; log full request body on Ollama 500
- Strengthen system prompt to require 3-4 tool calls before final answer
- Try fallback server when checking model capabilities (primary-only check caused 500 for models only on fallback)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ai/handlers.rs

@@ -304,6 +304,10 @@ pub async fn generate_agentic_insight_handler(
                 HttpResponse::BadRequest().json(serde_json::json!({
                     "error": format!("Failed to generate agentic insight: {}", error_msg)
                 }))
+            } else if error_msg.contains("error parsing tool call") {
+                HttpResponse::BadRequest().json(serde_json::json!({
+                    "error": "Model is not compatible with Ollama's tool calling protocol. Try a model known to support native tool calling (e.g. llama3.1, llama3.2, qwen2.5, mistral-nemo)."
+                }))
             } else {
                 HttpResponse::InternalServerError().json(serde_json::json!({
                     "error": format!("Failed to generate agentic insight: {}", error_msg)