docs: update all documentation for subscription auth, billing tiers, and API key management

packages/sdk-python/README.md

@@ -12,6 +12,8 @@ AgentLens is an observability SDK for AI agents. Unlike generic LLM tracing tool
 
 ## Quick Start
 
+First, create an account at [agentlens.vectry.tech/register](https://agentlens.vectry.tech/register) and generate an API key in **Settings > API Keys** in the dashboard.
+
 ```bash
 pip install vectry-agentlens
 ```
@@ -19,7 +21,7 @@ pip install vectry-agentlens
 ```python
 import agentlens
 
-# Initialize once at startup
+# Initialize with the API key from Settings > API Keys
 agentlens.init(api_key="your-api-key")
 
 # Trace any function with a decorator
@@ -160,7 +162,7 @@ Initialize the SDK. Call once at application startup.
 
 ```python
 agentlens.init(
-    api_key="your-api-key",           # Required. Your AgentLens API key.
+    api_key="your-api-key",           # Required. Create at Settings > API Keys in the dashboard.
     endpoint="https://...",            # API endpoint (default: https://agentlens.vectry.tech)
     flush_interval=5.0,               # Seconds between batch flushes (default: 5.0)
     max_batch_size=10,                 # Traces per batch before auto-flush (default: 10)
@@ -168,6 +170,8 @@ agentlens.init(
 )
 ```
 
+You can also set the API key via the `AGENTLENS_API_KEY` environment variable instead of passing it directly.
+
 ### `agentlens.trace()`
 
 Decorator or context manager that creates a trace (or a nested span if already inside a trace).
@@ -264,13 +268,25 @@ The SDK is lightweight and non-blocking. Traces are serialized and batched in a
 
 ## Dashboard
 
-View your traces at [agentlens.vectry.tech](https://agentlens.vectry.tech):
+View your traces at [agentlens.vectry.tech](https://agentlens.vectry.tech) (login required):
 
 - **Decision Trees** - Visualize the full decision path of every agent run
 - **Analytics** - Token usage, cost breakdowns, latency percentiles
 - **Real-time Streaming** - Watch agent decisions as they happen
 - **Session Grouping** - Track multi-turn conversations by session ID
 
+## Billing
+
+Each trace counts as one session for billing. AgentLens cloud offers three tiers:
+
+| Plan | Price | Sessions |
+|------|-------|----------|
+| Free | $0 | 20 sessions/day |
+| Starter | $5/month | 1,000 sessions/month |
+| Pro | $20/month | 100,000 sessions/month |
+
+Manage your subscription in **Settings > Billing**. Self-hosted instances have no session limits.
+
 ## Development
 
 ```bash