Add run.sh and fix run_tests.sh to use user's cargo cache

Add run.sh script to start the backend (erases db, runs cargo with sudo
using user's CARGO_HOME to avoid full recompilation). Remove sudo from
cargo test in run_tests.sh for the same reason.

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

backend/run.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+sudo rm -f oott.db
+sudo CARGO_HOME=$HOME/.cargo cargo run

backend/run_tests.sh

@@ -1,3 +1,3 @@
 #!/bin/sh
 sudo rm -f oott.db
-sudo cargo test -- --show-output
+cargo test -- --show-output