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/bin/reembed_embeddings.rs

@@ -1,7 +1,7 @@
 //! Re-embed stored corpora through `LocalLlm`, i.e. the same
-//! `LLM_BACKEND` dispatch the query side uses. The original import /
+//! `backend` (llm.toml) dispatch the query side uses. The original import /
 //! backfill tools always embedded via Ollama, so a deploy running
-//! `LLM_BACKEND=llamacpp` queries vector spaces the corpora may not live
+//! `backend = "llamacpp"` queries vector spaces the corpora may not live
 //! in. Three tables share the problem and are all covered here:
 //!
 //! - `daily_conversation_summaries` — re-embeds
@@ -30,7 +30,7 @@ use image_api::bin_progress;
 use std::env;
 
 #[derive(Parser, Debug)]
-#[command(author, version, about = "Re-embed stored corpora via the configured LLM_BACKEND", long_about = None)]
+#[command(author, version, about = "Re-embed stored corpora via the configured local backend", long_about = None)]
 struct Args {
     /// Comma-separated tables to process: summaries, calendar, search, entities
     #[arg(long, default_value = "summaries,calendar,search,entities")]
@@ -195,12 +195,12 @@ async fn reembed_table(
         };
 
         // The whole pipeline (DAO checks, stored corpora) assumes
-        // EMBEDDING_DIM dims. A mismatch means the active embed slot is not
+        // embedding.dim dims. A mismatch means the active embed slot is not
         // serving the configured model — stop rather than corrupt the table.
         anyhow::ensure!(
             new_emb.len() == image_api::ai::embedding_dim(),
             "backend returned {}-dim embedding (expected {}) — '{}' does not \
-             match the configured EMBEDDING_DIM",
+             match the configured embedding.dim",
             new_emb.len(),
             image_api::ai::embedding_dim(),
             llm.embedding_model_version()