Add configuration from toml file

config.md

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+# WeaselDB Configuration
+
+WeaselDB uses a TOML configuration file to control server behavior and API limits. The configuration is organized into three main sections that correspond to different aspects of the system.
+
+## Configuration File Location
+
+By default, WeaselDB looks for `config.toml` in the current directory. You can specify an alternative path:
+
+```bash
+./weaseldb /path/to/custom/config.toml
+```
+
+## Configuration Sections
+
+### Server Configuration (`[server]`)
+
+Controls basic server binding and request limits.
+
+| Parameter | Type | Default | Description |
+|-----------|------|---------|-------------|
+| `bind_address` | string | `"127.0.0.1"` | IP address to bind the server to |
+| `port` | integer | `8080` | Port number to listen on |
+| `max_request_size_bytes` | integer | `1048576` (1MB) | Maximum size for incoming requests. Requests exceeding this limit receive a `413 Content Too Large` response |
+
+### Commit Configuration (`[commit]`)
+
+Controls behavior of the `/v1/commit` endpoint and request ID management.
+
+| Parameter | Type | Default | Description |
+|-----------|------|---------|-------------|
+| `min_request_id_length` | integer | `20` | Minimum length required for client-provided `request_id` fields to ensure sufficient entropy for collision avoidance |
+| `request_id_retention_hours` | integer | `24` | How long to retain request IDs in memory for `/v1/status` queries. Longer retention reduces the chance of `log_truncated` responses |
+| `request_id_retention_versions` | integer | `100000000` | Minimum number of versions to retain request IDs for, regardless of time. Provides additional protection against `log_truncated` responses |
+
+### Subscription Configuration (`[subscription]`)
+
+Controls behavior of the `/v1/subscribe` endpoint and SSE streaming.
+
+| Parameter | Type | Default | Description |
+|-----------|------|---------|-------------|
+| `max_buffer_size_bytes` | integer | `10485760` (10MB) | Maximum amount of unconsumed data to buffer for slow subscribers. Connections are closed if this limit is exceeded |
+| `keepalive_interval_seconds` | integer | `30` | Interval between keepalive comments in the Server-Sent Events stream to prevent idle timeouts on network proxies |
+
+## Example Configuration
+
+```toml
+# WeaselDB Configuration File
+
+[server]
+bind_address = "0.0.0.0"
+port = 8080
+max_request_size_bytes = 2097152  # 2MB
+
+[commit]
+min_request_id_length = 32
+request_id_retention_hours = 48
+request_id_retention_versions = 50000
+
+[subscription]
+max_buffer_size_bytes = 52428800  # 50MB
+keepalive_interval_seconds = 15
+```
+
+## Configuration Loading
+
+- If the specified config file doesn't exist or contains errors, WeaselDB will use default values and log a warning
+- All configuration parameters are optional - any missing values will use the defaults shown above
+
+## API Relationship
+
+These configuration parameters directly affect API behavior:
+
+- **`max_request_size_bytes`**: Determines when `/v1/commit` returns `413 Content Too Large`
+- **`min_request_id_length`**: Validates `request_id` fields in `/v1/commit` requests
+- **`request_id_retention_*`**: Affects availability of data for `/v1/status` queries and likelihood of `log_truncated` responses
+- **`max_buffer_size_bytes`**: Controls when `/v1/subscribe` connections are terminated due to slow consumption
+- **`keepalive_interval_seconds`**: Frequency of keepalive comments in `/v1/subscribe` streams