Add discovery phase to /plan-issues workflow

The planning process previously jumped directly from understanding a feature
to breaking it down into issues. This led to proposing issues without first
understanding the user's actual workflow and where the gaps are.

Added a discovery phase that requires walking through:
- Who is the specific user
- What is their goal
- Step-by-step workflow to reach the goal
- What exists today
- Where the workflow breaks or has gaps
- What's the MVP

Issues are now derived from workflow gaps rather than guessing.

Closes #29

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

skills/roadmap-planning/SKILL.md

@@ -15,7 +15,33 @@ How to plan features and create issues for implementation.
 - Who benefits and how?
 - What's the success criteria?
 
-### 2. Break Down the Work
+### 2. Discovery Phase
+
+Before breaking down work into issues, understand the user's workflow:
+
+| Question | Why It Matters |
+|----------|----------------|
+| **Who** is the user? | Specific persona, not "users" |
+| **What's their goal?** | The job they're trying to accomplish |
+| **What's their workflow?** | Step-by-step actions to reach the goal |
+| **What exists today?** | Current state and gaps |
+| **What's the MVP?** | Minimum to deliver value |
+
+**Walk through the workflow step by step:**
+1. User starts at: [starting point]
+2. User does: [action 1]
+3. System responds: [what happens]
+4. User does: [action 2]
+5. ... continue until goal is reached
+
+**Identify the gaps:**
+- Where does the workflow break today?
+- Which steps are missing or painful?
+- What's the smallest change that unblocks value?
+
+**Derive issues from workflow gaps** - not from guessing what might be needed. Each issue should address a specific gap in the user's workflow.
+
+### 3. Break Down the Work
 - Identify distinct components
 - Define boundaries between pieces
 - Aim for issues that are:
@@ -23,12 +49,12 @@ How to plan features and create issues for implementation.
   - Independently testable
   - Clear in scope
 
-### 3. Identify Dependencies
+### 4. Identify Dependencies
 - Which pieces must come first?
 - What can be parallelized?
 - Are there external blockers?
 
-### 4. Create Issues
+### 5. Create Issues
 - Follow issue-writing patterns
 - Reference dependencies explicitly
 - Use consistent labeling