docs: add branching strategy - one feature per branch

- Each phase gets its own branch
- Branch from previous phase to inherit work
- Rebase onto main before creating PR
- Keeps history clean and reviews focused

CLAUDE.md

@@ -400,3 +400,100 @@ git rebase -i HEAD~2
 
 If you're writing a commit message that says "fixed typo from previous commit", you should have rebased instead.
 
+
+---
+
+## Part 6: Branching Strategy - One Feature Per Branch
+
+### The Workflow
+
+**Each phase/feature gets its own branch:**
+
+```
+main
+ └─ feature/03-design-polish (Phase 03)
+     └─ feature/04-workout-modification (Phase 04, branched from 03)
+         └─ feature/05-exercise-encyclopedia (Phase 05, branched from 04)
+```
+
+### Step-by-Step
+
+#### 1. Work on Phase 03
+```bash
+git checkout -b feature/03-design-polish
+# ... do all Phase 03 work ...
+# Multiple commits, testing, refinement
+git push origin feature/03-design-polish
+```
+
+#### 2. When Phase 03 is Done → Create PR
+```bash
+# Create PR: feature/03-design-polish → main
+# Get code review, merge when approved
+# This becomes the baseline for Phase 04
+```
+
+#### 3. Start Phase 04 (NEW BRANCH from Phase 03)
+```bash
+# First, make sure local is up-to-date
+git checkout feature/03-design-polish
+git pull origin feature/03-design-polish
+
+# Create new branch FROM the current feature
+git checkout -b feature/04-workout-modification
+
+# Now do all Phase 04 work on this new branch
+# ... commits for 04-01, 04-02, 04-03, etc ...
+git push origin feature/04-workout-modification
+```
+
+#### 4. When Phase 04 is Done → Rebase Before PR
+```bash
+# Make sure feature/03 is merged to main
+git fetch origin
+
+# Rebase Phase 04 onto main (to get clean history)
+git rebase origin/main feature/04-workout-modification
+
+# Force-push (since we're rebasing)
+git push -f origin feature/04-workout-modification
+
+# Create PR: feature/04-workout-modification → main
+```
+
+### Why This Matters
+
+- ✅ **Cleaner history** — Each phase is separate
+- ✅ **Easier reviews** — PRs are focused on one phase
+- ✅ **Better testing** — Each phase tested independently
+- ✅ **Easy rollback** — Remove one phase without touching others
+- ✅ **Work in parallel** — Different agents can work on different phases
+
+### Current Situation
+
+We've mixed Phase 03 and 04 in `feature/03-design-polish`. Going forward:
+
+1. **Merge feature/03-design-polish → main** (code review, then merge)
+2. **Create feature/04-workout-modification** from main
+3. Move/cherry-pick Phase 04 commits to new branch (or just continue from here)
+4. **Create feature/05-exercise-encyclopedia** from feature/04 when 04 is done
+
+### Rebase Chain Example
+
+```bash
+# After 03 is merged and 04 starts:
+git checkout feature/04-workout-modification
+git rebase origin/main  # Rebase 04 onto latest main
+
+# After 04 is merged and 05 starts:
+git checkout feature/05-exercise-encyclopedia
+git rebase origin/main  # Always rebase new features onto main
+```
+
+### Rule of Thumb
+
+- **One feature per branch**
+- **Each branch is independent**
+- **Rebase onto main before PR**
+- **No "feature/03-design-polish" commits after it's merged**
+