docs: add stepOptions to project configuration

The stepOptions feature was implemented in probitas.json but was missing
from the Configuration.md documentation. This caused confusion about how
to set default timeout and retry behavior at the project level.

Added three documentation updates:
- Configuration example showing stepOptions structure
- Table entry for stepOptions in configuration options
- Detailed section explaining stepOptions behavior and override precedence

The documentation now aligns with the implementation in probitas/src/cli/types.ts
and the example in probitas/assets/probitas.jsonc.

Author: lambdalisue

docs/configuration.md

@@ -34,6 +34,14 @@ The first file found is used. JSONC files support `//` and `/* */` comments.
   "maxFailures": 0,
   // Default timeout for scenarios
   "timeout": "30s",
+  // Default step options for all scenarios
+  "stepOptions": {
+    "timeout": 30000,
+    "retry": {
+      "maxAttempts": 1,
+      "backoff": "linear"
+    }
+  },
   // Default selectors for filtering scenarios
   "selectors": ["!tag:wip"]
 }
@@ -47,6 +55,7 @@ The first file found is used. JSONC files support `//` and `/* */` comments.
 | `maxConcurrency` | Maximum parallel scenario execution       | unlimited (`0`)                       |
 | `maxFailures`    | Maximum failures before stopping          | unlimited (`0`)                       |
 | `timeout`        | Default timeout for scenarios             | `"30s"`                               |
+| `stepOptions`    | Default step options (timeout, retry)     | See [stepOptions](#stepOptions)       |
 | `selectors`      | Default selectors for filtering scenarios | `[]`                                  |
 
 \*Default exclude patterns:
@@ -70,6 +79,44 @@ Controls when the test runner stops execution:
 }
 ```
 
+### stepOptions
+
+Set default timeout and retry behavior for all steps across all scenarios. These
+defaults can be overridden at the scenario level or individual step level.
+
+```jsonc
+{
+  "stepOptions": {
+    // Default timeout for each step in milliseconds
+    "timeout": 30000,
+    // Default retry configuration for transient failures
+    "retry": {
+      // Maximum retry attempts (1 = no retry)
+      "maxAttempts": 3,
+      // Backoff strategy: "linear" or "exponential"
+      "backoff": "exponential"
+    }
+  }
+}
+```
+
+| Option              | Description                                     | Default    |
+| ------------------- | ----------------------------------------------- | ---------- |
+| `timeout`           | Step timeout in milliseconds                    | `30000`    |
+| `retry.maxAttempts` | Maximum retry attempts (1 = no retry)           | `1`        |
+| `retry.backoff`     | Backoff strategy: `"linear"` or `"exponential"` | `"linear"` |
+
+These project-level defaults apply to all scenarios unless overridden. Override
+precedence (highest to lowest):
+
+1. Individual step options (highest priority)
+2. Scenario-level `stepOptions`
+3. Project-level `stepOptions` (this setting)
+4. Framework defaults (lowest priority)
+
+See [Scenario Options](#scenario-options) and [Step Options](#step-options) for
+how to override these defaults.
+
 ### Selectors
 
 Selectors filter which scenarios to run. The format is `[!][type:]value`: