fix(workflow): consistent phase transition routing through discuss-phase (#530)

Three routing fixes:
- transition.md checks for CONTEXT.md before routing — discuss-phase when
  missing, plan-phase when present (matches progress.md behavior)
- execute-phase.md offer_next delegates to transition.md instead of emitting
  duplicate "Next Up" blocks
- discuss-phase.md adds explicit handling for "Other" free-text responses

Closes #530

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

get-shit-done/workflows/transition.md

@@ -358,10 +358,18 @@ This returns all phases with goals, disk status, and completion info.
 
 Read ROADMAP.md to get the next phase's name and goal.
 
+**Check if next phase has CONTEXT.md:**
+
+```bash
+ls .planning/phases/*[X+1]*/*-CONTEXT.md 2>/dev/null
+```
+
 **If next phase exists:**
 
 <if mode="yolo">
 
+**If CONTEXT.md exists:**
+
 ```
 Phase [X] marked complete.
 
@@ -372,10 +380,24 @@ Next: Phase [X+1] — [Name]
 
 Exit skill and invoke SlashCommand("/gsd:plan-phase [X+1]")
 
+**If CONTEXT.md does NOT exist:**
+
+```
+Phase [X] marked complete.
+
+Next: Phase [X+1] — [Name]
+
+⚡ Auto-continuing: Discuss Phase [X+1] first
+```
+
+Exit skill and invoke SlashCommand("/gsd:discuss-phase [X+1]")
+
 </if>
 
 <if mode="interactive" OR="custom with gates.confirm_transition true">
 
+**If CONTEXT.md does NOT exist:**
+
 ```
 ## ✓ Phase [X] Complete
 
@@ -385,6 +407,31 @@ Exit skill and invoke SlashCommand("/gsd:plan-phase [X+1]")
 
 **Phase [X+1]: [Name]** — [Goal from ROADMAP.md]
 
+`/gsd:discuss-phase [X+1]` — gather context and clarify approach
+
+<sub>`/clear` first → fresh context window</sub>
+
+---
+
+**Also available:**
+- `/gsd:plan-phase [X+1]` — skip discussion, plan directly
+- `/gsd:research-phase [X+1]` — investigate unknowns
+
+---
+```
+
+**If CONTEXT.md exists:**
+
+```
+## ✓ Phase [X] Complete
+
+---
+
+## ▶ Next Up
+
+**Phase [X+1]: [Name]** — [Goal from ROADMAP.md]
+<sub>✓ Context gathered, ready to plan</sub>
+
 `/gsd:plan-phase [X+1]`
 
 <sub>`/clear` first → fresh context window</sub>
@@ -392,9 +439,8 @@ Exit skill and invoke SlashCommand("/gsd:plan-phase [X+1]")
 ---
 
 **Also available:**
-- `/gsd:discuss-phase [X+1]` — gather context first
+- `/gsd:discuss-phase [X+1]` — revisit context
 - `/gsd:research-phase [X+1]` — investigate unknowns
-- Review roadmap
 
 ---
 ```