Phase 39 (first slice): Ollama Cloud adapter on /v1/chat

Second provider wired. /v1/chat now routes by optional `provider`
field: default "ollama" hits local via sidecar, "ollama_cloud"
(or "cloud") hits ollama.com/api/generate directly with Bearer auth.
Key sourced at gateway startup from OLLAMA_CLOUD_KEY env, then
/root/llm_team_config.json (providers.ollama_cloud.api_key), then
OLLAMA_CLOUD_API_KEY env. Config source matches LLM Team convention.

Shape-identical to scenario.ts::generateCloud — same endpoint, same
body, same Bearer auth. Cloud path bypasses sidecar entirely (sidecar
is local-only by design, mirrors TS agent.ts).

Changes:
- crates/gateway/src/v1/ollama_cloud.rs (new, 130 LOC) — reqwest
  client, resolve_cloud_key(), chat() adapter, CloudGenerateBody /
  CloudGenerateResponse wire shapes
- crates/gateway/src/v1/ollama.rs — flatten_messages_public()
  re-export so sibling adapters reuse the shape collapse
- crates/gateway/src/v1/mod.rs — provider field on ChatRequest,
  dispatch match in chat() handler, ollama_cloud_key on V1State
- crates/gateway/src/main.rs — resolves cloud key at startup,
  logs which source provided it
- crates/gateway/Cargo.toml — reqwest 0.12 with rustls-tls

Verified end-to-end after restart:
- provider=ollama → qwen3.5:latest local (~400ms, Phase 38 unchanged)
- provider=ollama_cloud + model=gpt-oss:120b → real 225-word
  technical response in 5.4s, 313 tokens

Tests: 9/9 green (7 from Phase 38 + 2 new for cloud body serialization
and key resolver shape).

Not in this slice: trait extraction (full Phase 39 scope adds
ProviderAdapter trait + OpenRouter adapter + fallback chain logic).
These land next with Phase 40 routing engine on top.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/gateway/src/v1/ollama.rs

@@ -74,6 +74,14 @@ pub async fn chat(client: &AiClient, req: &ChatRequest) -> Result<ChatResponse,
     })
 }
 
+/// Public re-export of the flattener so sibling adapters (Ollama Cloud,
+/// future OpenRouter) can reuse the same shape collapse without
+/// duplicating the logic. Keeps `(system, prompt)` format consistent
+/// across providers.
+pub fn flatten_messages_public(messages: &[Message]) -> (String, String) {
+    flatten_messages(messages)
+}
+
 /// Collapse a message array into (system, prompt). Multiple system
 /// messages concatenate with a newline — matches OpenAI's documented
 /// behavior. Non-system messages become role-labeled turns.