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>

commands/plan-issues.md

@@ -16,12 +16,24 @@ context: fork
 3. **Identify job**: Which job to be done does this enable?
 4. **Understand the feature**: Analyze what "$1" involves
 5. **Explore the codebase** if needed to understand context
-6. **Break down** into discrete, actionable issues:
+
+6. **Discovery phase**: Before proposing issues, walk through the user workflow:
+   - Who is the specific user?
+   - What is their goal?
+   - What is their step-by-step workflow to reach that goal?
+   - What exists today?
+   - Where does the workflow break or have gaps?
+   - What's the MVP that delivers value?
+   
+   Present this as a workflow walkthrough before proposing any issues.
+
+7. **Break down** into discrete, actionable issues:
+   - Derive issues from the workflow gaps identified in discovery
    - Each issue should be independently completable
    - Clear dependencies between issues
    - Appropriate scope (not too big, not too small)
 
-7. **Present the plan** (include vision alignment if vision exists):
+8. **Present the plan** (include vision alignment if vision exists):
    ```
    ## Proposed Issues for: $1
 
@@ -30,12 +42,15 @@ context: fork
    Supports: [Milestone/Goal name]
 
    1. [Title] - Brief description
+      Addresses gap: [which workflow gap this solves]
       Dependencies: none
 
    2. [Title] - Brief description
+      Addresses gap: [which workflow gap this solves]
       Dependencies: #1
 
    3. [Title] - Brief description
+      Addresses gap: [which workflow gap this solves]
       Dependencies: #1, #2
    ```
 
@@ -45,7 +60,7 @@ context: fork
    - This should be added as a non-goal
    - Proceed anyway (with justification)
 
-8. **Ask for approval** before creating issues
-9. **Create issues** in dependency order (blockers first)
-10. **Link dependencies** using `tea issues deps add <issue> <blocker>` for each dependency
-11. **Present summary** with links to created issues and dependency graph
+9. **Ask for approval** before creating issues
+10. **Create issues** in dependency order (blockers first)
+11. **Link dependencies** using `tea issues deps add <issue> <blocker>` for each dependency
+12. **Present summary** with links to created issues and dependency graph