new tasks, devnet topup, cli, new model support

QUICKSTART.md

@@ -54,6 +54,7 @@ on the host firewall if other machines will join:
 
 ```bash
 .venv/bin/meshnet-tracker start --host 0.0.0.0 --port 8080
+# --starting-credit 1 --devnet-topup 10
 ```
 
 Verify from the tracker host:
@@ -514,6 +515,7 @@ Send inference through the tracker (which picks the head node and injects the ro
 ```bash
 curl -s https://ai.neuron.d-popov.com/v1/chat/completions \
   -H "Content-Type: application/json" \
+  -H "Authorization: Bearer sk-mesh-<your-key>" \
   -d '{
     "model": "Qwen/Qwen2.5-0.5B-Instruct",
     "messages": [{"role": "user", "content": "What is 7 times 8?"}],
@@ -529,6 +531,47 @@ curl -s http://localhost:7001/v1/chat/completions \
   -d '{"model": "Qwen/Qwen2.5-0.5B-Instruct", "messages": [{"role": "user", "content": "Hi"}]}'
 ```
 
+## Accounts, API keys, and credit (billing-enabled trackers)
+
+Public trackers run with billing on: `/v1/chat/completions` requires a real
+API key from a registered account. Unknown bearer strings get `401`; a key
+with no balance gets `402 insufficient balance`.
+
+**Dashboard flow (easiest):** open `https://<tracker>/dashboard`, register with
+an email + password, then click **+ new key**. The key (`sk-mesh-…`) shows its
+balance next to it. If the tracker was started with `--starting-credit`, your
+first key arrives pre-funded (Caller Credit, once per account). If it was
+started with `--devnet-topup`, every key row has a **+$N (devnet)** button to
+refill during testing.
+
+**Curl flow:**
+
+```bash
+# 1. Register (once)
+curl -s https://<tracker>/v1/auth/register \
+  -H "Content-Type: application/json" \
+  -d '{"email": "you@example.com", "password": "hunter22-or-better"}'
+# → {"session_token": "...", ...}
+
+# 2. Create an API key (session token from step 1)
+curl -s https://<tracker>/v1/account/keys -X POST \
+  -H "Authorization: Bearer <session_token>"
+# → {"api_key": "sk-mesh-...", "caller_credit_granted": true}
+
+# 3. Check balance / usage
+curl -s https://<tracker>/v1/account -H "Authorization: Bearer <session_token>"
+
+# 4. (devnet trackers only) top up a key
+curl -s https://<tracker>/v1/account/topup -X POST \
+  -H "Authorization: Bearer <session_token>" \
+  -H "Content-Type: application/json" \
+  -d '{"api_key": "sk-mesh-..."}'
+```
+
+Operator side: both features default to 1 USDT (`--starting-credit` /
+`--devnet-topup`). Set both to 0 on mainnet deployments — real deposits flow
+through the on-chain USDT treasury watcher instead.
+
 ---
 
 ## Step 1 — Start the tracker (Terminal 1)