docs: document llm.toml and llama-swap metadata discovery

README, CLAUDE.md and .env.example now point at llm.toml for LLM settings
(OPENROUTER_API_KEY stays in env) and describe the legacy env override
window, the discovered picker and the startup cross-check. ADR-0003 records
the move and amends ADR-0002's deployment-config home; CONTEXT.md's
Deployment config / Hard default entries follow. Source comments and the
"set LLAMA_SWAP_URL" error strings name the llm.toml keys.

Also fixes README's AGENTIC_MAX_ITERATIONS default (10 -> 12, what the
code uses).

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

src/state.rs

@@ -70,9 +70,9 @@ pub struct AppState {
     #[allow(dead_code)]
     pub openrouter: Option<Arc<OpenRouterClient>>,
     /// Curated list of OpenRouter model ids exposed to clients. Sourced from
-    /// `OPENROUTER_ALLOWED_MODELS` (comma-separated). Empty when unset.
+    /// `openrouter.allowed`. Empty when unset.
     pub openrouter_allowed_models: Vec<String>,
-    /// `None` when `LLAMA_SWAP_URL` is not configured. Consulted only when a
+    /// `None` when `llamacpp.url` is not configured. Consulted only when a
     /// request explicitly opts into `backend=llamacpp`. Same shape as the
     /// `openrouter` slot — present here so handlers can route to it without
     /// threading through the generator.