breadmill/breadsearch: narrow embedder lock scope, recover from poisoned mutexes, atomic index save + corrupt rebuild, fix GUI busy-poll, bump theme pin

- indexer.rs: embedder mutex is now locked only around each chunk's
  embed_document() call instead of the whole file's chunk loop, so a slow
  MIGraphX JIT compile on one file no longer blocks every query for minutes
- sync_ext.rs (new)/indexer.rs/main.rs/serve.rs: added MutexExt::lock_recover(),
  replacing every .lock().unwrap() so a panic on one thread (poisoning the
  mutex) logs a warning and recovers instead of cascading into every future
  lock().unwrap() call
- store.rs: save_index now writes to a .tmp sibling and renames atomically
  into place; Store::open recovers from an index that fails to load by
  wiping it and the SQLite files/chunks tables so the next scan rebuilds
  from scratch, instead of refusing to start at all. Note: this recovery
  only catches corruption usearch's loader reports as Err — verified
  experimentally that sufficiently garbled input segfaults the process
  instead, which no Rust-side handling can catch; the atomic save is what
  actually prevents the realistic mid-crash corruption case from arising
- breadsearch/src/main.rs: GUI query-result wait switched from
  glib::idle_add_local (re-invoked every main-loop tick, pegging a core for
  the whole wait) to a 15ms glib::timeout_add_local poll
- breadsearch/Cargo.toml: bread-theme pin bumped v0.2.8 -> v0.2.10 to match
  the rest of the family

breadmill/src/main.rs

@@ -13,10 +13,12 @@ mod indexer;
 mod power;
 mod serve;
 mod store;
+mod sync_ext;
 
 use embed::{Backend, OrtEmbedder};
 use indexer::{Indexer, SharedState};
 use store::Store;
+use sync_ext::MutexExt;
 
 const MODEL_URL: &str =
     "https://huggingface.co/nomic-ai/nomic-embed-text-v1.5/resolve/main/onnx/model.onnx";
@@ -170,7 +172,7 @@ fn run_daemon(
             eprintln!("breadmill: loading model...");
             match OrtEmbedder::load(&model_path, &tokenizer_path, dim, backend) {
                 Ok(embedder) => {
-                    *state_clone.embedder.lock().unwrap() = Some(embedder);
+                    *state_clone.embedder.lock_recover() = Some(embedder);
                     state_clone.model_ready.store(true, Ordering::Relaxed);
                     eprintln!("breadmill: model loaded");
                 }