feat(docs): add bridge documentation for early access (#20188)

examples/monitoring/dashboards/grafana/aibridge/README.md

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+# AI Bridge Grafana Dashboard
+
+![AI Bridge example Grafana Dashboard](./grafana_dashboard.png)A sample Grafana dashboard for monitoring AI Bridge token usage, costs, and cache hit rates in Coder.
+
+The dashboard includes three main sections with multiple visualization panels:
+
+**Usage Leaderboards** - Track token consumption across your organization:
+- Bar chart showing input, output, cache read, and cache write tokens per user
+- Total usage statistics with breakdowns by token type
+
+**Approximate Cost Table** - Estimate AI spending by joining token usage with live pricing data from LiteLLM:
+- Per-provider and per-model cost breakdown
+- Input, output, cache read, and cache write costs
+- Total cost calculations with footer summaries
+
+**Interceptions** - Monitor AI API calls over time:
+- Time-series bar chart of interceptions by user
+- Total interception count
+
+**Prompts & Tool Calls Details** - Inspect actual AI interactions:
+- User Prompts table showing all prompts sent to AI models with timestamps
+- Tool Calls table displaying MCP tool invocations, inputs, and errors (color-coded for failures)
+
+All panels support filtering by time range, username, provider (Anthropic, OpenAI, etc.), and model using regex patterns.
+
+## Setup
+
+1. **Install the Infinity plugin**: `grafana-cli plugins install yesoreyeram-infinity-datasource`
+
+2. **Configure data sources**:
+   - **PostgreSQL datasource** (`coder-observability-ro`): Connect to your Coder database with read access to `aibridge_interceptions`, `aibridge_token_usages`, `aibridge_user_prompts`, `aibridge_tool_usages` and `users`
+   - **Infinity datasource** (`litellm-pricing-data`): Point to `https://raw.githubusercontent.com/BerriAI/litellm/refs/heads/main/model_prices_and_context_window.json` for model pricing data
+
+3. **Import**: Download [`dashboard.json`](https://raw.githubusercontent.com/coder/coder/main/examples/monitoring/dashboards/grafana/aibridge/dashboard.json) from this directory, then in Grafana navigate to **Dashboards** → **Import** → **Upload JSON file**. Map the data sources when prompted.
+
+## Features
+
+- Token usage leaderboards by user, provider, and model
+- Filterable by time range, username, provider, and model (regex supported)