Separate install from start — detect if build needed

[joelteply]

Problem

npm start does everything: deps check, Rust build, model downloads, TS build, browser build, worker startup, DB check, seeding, browser open. Takes 70-150s every time.

Desired behavior

• npm install → full install (deps, builds, models, DB setup). Run once or when needed.
• npm start → just start services + open browser. Fast (<10s if everything built).
• Detection: check if binaries exist, models exist, DB exists. If missing, tell user to run npm install.

Current pain

Every restart rebuilds everything. After a reboot, postgres isn't running and the startup hangs. Install concerns mixed with runtime concerns.

[joelteply]

Addressed by install.sh (PR #428). Full setup separated from runtime: install.sh handles deps/config/build, npm start handles runtime. install.sh runs prereq checks that npm install doesn't. Startup speed optimization (skip builds when cached) is a separate concern.