fix: auto-discover PRD in validate-prd instead of always asking (#1619)

When only one PRD exists in planning_artifacts, use it automatically
instead of prompting the user for its path. Still asks when multiple
PRDs are found or falls back to manual input when none are discovered.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/bmm/workflows/2-plan-workflows/create-prd/steps-v/step-v-01-discovery.md

@@ -70,14 +70,22 @@ This file contains the BMAD PRD philosophy, standards, and validation criteria t
 **If PRD path provided as invocation parameter:**
 - Use provided path
 
-**If no PRD path provided:**
-"**PRD Validation Workflow**
+**If no PRD path provided, auto-discover:**
+- Search `{planning_artifacts}` for files matching `*prd*.md`
+- Also check for sharded PRDs: `{planning_artifacts}/*prd*/*.md`
 
-Which PRD would you like to validate?
+**If exactly ONE PRD found:**
+- Use it automatically
+- Inform user: "Found PRD: {discovered_path} — using it for validation."
 
-Please provide the path to the PRD file you want to validate."
+**If MULTIPLE PRDs found:**
+- List all discovered PRDs with numbered options
+- "I found multiple PRDs. Which one would you like to validate?"
+- Wait for user selection
 
-**Wait for user to provide PRD path.**
+**If NO PRDs found:**
+- "I couldn't find any PRD files in {planning_artifacts}. Please provide the path to the PRD file you want to validate."
+- Wait for user to provide PRD path.
 
 ### 3. Validate PRD Exists and Load
 

src/bmm/workflows/2-plan-workflows/create-prd/workflow-validate-prd.md

@@ -60,6 +60,4 @@ Load and read full config from {main_config} and resolve:
 
 "**Validate Mode: Validating an existing PRD against BMAD standards.**"
 
-Prompt for PRD path: "Which PRD would you like to validate? Please provide the path to the PRD.md file."
-
 Then read fully and follow: `{validateWorkflow}` (steps-v/step-v-01-discovery.md)