Extract lib.rs, inline search in memory-search hook

Create lib.rs so all binaries can share library code directly instead
of shelling out to poc-memory. memory-search now calls search::search()
and store::Store::load() in-process instead of Command::new("poc-memory").

The load-context call still shells out (needs get_group_content moved
from main.rs to a library module).

Also: add search::format_results(), deduplicate extract_query_terms.

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

Cargo.toml

@@ -39,6 +39,10 @@ reqwest = { version = "0.12", default-features = false, features = ["rustls-tls-
 [build-dependencies]
 capnpc = "0.20"
 
+[lib]
+name = "poc_memory"
+path = "src/lib.rs"
+
 [[bin]]
 name = "poc-memory"
 path = "src/main.rs"