feat: show Sign in CTA when dotli has no session

[tallesborges]

Why

Cold-start (fresh browser, RevX/WebContainer preview, any session where dotli isn't paired) shows this raw error before the user can do anything:

Failed to connect: Unknown: RequestCredentialsErr::NotConnected: RequestCredentials: not connected

That's dotli's correct behavior — its handleAccountGet returns NotConnected whenever there's no authenticated session. The SPA just wasn't surfacing it as a normal UI state.

What

• Catch RequestCredentialsErr.NotConnected (instanceof — the codec-error class defines Symbol.hasInstance) and route to a new signed-out status instead of error.
• New signIn() helper: calls accountsProvider.requestLogin(...) then re-runs connectAccount(). On rejected, the next accountGet returns NotConnected again and the UI lands back on the sign-in screen — no special-case branch needed.
• App.tsx renders "Sign in to dotli to play Rock Paper Scissors." + a Sign in button when status === "signed-out". Other states (idle, connecting, ready, error) unchanged.

24 insertions, 2 deletions across two files.

Flow

1. Open SPA → accountGet returns NotConnected → state goes to signed-out → CTA renders.
2. Click Sign in → requestLogin opens dotli's QR / PAPP pairing UI → user pairs → connectAccount retries → game loads.

Not in scope

No accountConnectionStatusSubscribe subscription. Two edge cases that gracefully degrade without it:

• User signs in via dotli's topbar instead of clicking our button → SPA stays on the sign-in screen until they click; requestLogin then returns alreadyConnected instantly.
• User signs out of dotli mid-session → SPA keeps the ready UI until next call fails; recovers on retry.

Easy to add the subscription later if either becomes a real friction point.

Verified

• Vite build clean (bunx vite build).
• Note: bun run build:frontend is currently red on main because of a pre-existing TS2554 in the 9aea38a fix sign tx commit (getProductAccountSigner(productAccount, "createTransaction") — the second arg requires @novasamatech/product-sdk ≥ 0.7.9-5, but package.json pins 0.7.8-2). Unrelated to this PR, worth raising separately.