fix(dev-agent): Adopt Fibonacci scale for complexity assessment

This commit updates the complexity assessment system from a 1-10 scale to the industry-standard Fibonacci scale (1, 2, 3, 5, 8, 13), aligning BMAD with Agile best practices.

Key changes:
- Updated agentThresholdStory from 6 to 5 (Fibonacci equivalent)
- Updated agentThresholdTask from 7 to 8 (Fibonacci equivalent)
- Added Fibonacci complexity guidelines to help agents make consistent assessments
- Modified task instructions to reference Fibonacci scale instead of 1-10

This change ensures consistency with industry standards that most development teams already understand, while maintaining the same relative complexity thresholds for triggering review processes.

bmad-core/core-config.yml

@@ -18,9 +18,9 @@ devLoadAlwaysFiles:
 devDebugLog: .ai/debug-log.md
 devStoryLocation: docs/stories
 agentCoreDump: .ai/core-dump{n}.md
-# Thresholds for the dev agent's integrated review process (Scale 1-10).
+# Thresholds for the dev agent's integrated review process (Fibonacci Scale: 1,2,3,5,8,13).
 # The agent will enter "Review Mode" if a story's complexity exceeds agentThresholdStory.
 # Within Review Mode, it will trigger a self-critique loop for any task whose
 # complexity exceeds agentThresholdTask.
-agentThresholdStory: 6
-agentThresholdTask: 7
+agentThresholdStory: 5
+agentThresholdTask: 8

bmad-core/tasks/implement-story-with-review.md

@@ -26,11 +26,19 @@ To execute a user story with a proactive analysis and review cycle, ensuring ali
         3. **Request explicit instruction to continue:** "Please let me know how you would like to proceed."
         4. **HALT and await user response.** Once the user confirms to continue (with or without them enabling internet access), proceed to the next step using the available knowledge.]]
 5.  **Initial Complexity Assessment & Mode Declaration**:
-    -   Calculate a "Story Complexity" score from 1 to 10.
+    -   Calculate a "Story Complexity" score using Fibonacci scale (1, 2, 3, 5, 8, 13).
     -   If Review Mode was forced by the user OR if `Story Complexity` > `agentThresholdStory`, declare: "**Entering high-scrutiny 'Review Mode' for this story. Each task will be individually assessed.**"
     -   Otherwise, declare: "**Story complexity is within standard limits. Each task will still be individually assessed for complexity.**"
     -   Log the complexity score (if calculated) and the reason for the mode in the story's `Dev Notes`.
 
+**Fibonacci Complexity Guidelines:**
+- **1**: Trivial changes (typos, simple styling)
+- **2**: Minor feature additions (new button, basic validation)
+- **3**: Standard feature implementation (form handling, API calls)
+- **5**: Complex features (authentication, data processing)
+- **8**: Major architectural changes (new services, database schema)
+- **13**: High-risk/high-uncertainty work (new frameworks, complex integrations)
+
 ## 2. Unified Task Execution Phase
 
 [[LLM: Proceed with the `Tasks / Subtasks` list from the story file one by one. The following logic applies to EVERY task.]]
@@ -38,7 +46,7 @@ To execute a user story with a proactive analysis and review cycle, ensuring ali
 << For each task in the story's task list: >>
 
 1.  **Mandatory Task Complexity Assessment**:
-    -   Evaluate the complexity of the *current task* on a scale of 1-10, leveraging the initial semantic search results.
+    -   Evaluate the complexity of the *current task* using Fibonacci scale (1, 2, 3, 5, 8, 13), leveraging the initial semantic search results.
     -   Compare the `Task Complexity` score against the `agentThresholdTask` value from `core-config.yml`.
 
 2.  **Conditional Implementation Path**: