fix(profiles): rename checkpoint to context-save in 5 profiles

gstack upstream renamed the `checkpoint` skill to `context-save`
(it was shadowed by Claude Code's native /checkpoint rewind alias).
`/profile set full|dev|backend|web|web-full` was emitting
`⚠ missing: checkpoint — try: bash link.sh`, but link.sh only
materializes symlinks for skills that exist upstream — it cannot
resurrect a renamed skill, so the suggested next step was a dead
end.

Replace `checkpoint` → `context-save` in all 5 affected profiles
so the warning goes away and the new skill is enabled when the
profile is applied.

CLAUDE.md routing rule (line 193) also updated locally but left
uncommitted because the file carries an unrelated in-progress
graphify section rewrite.

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

lib/profiles/backend.profile

@@ -16,7 +16,7 @@ analyze                           personal
 # Ship + review + land
 ship
 review
-checkpoint
+context-save
 land-and-deploy
 
 # Second opinion for hard problems

lib/profiles/dev.profile

@@ -20,5 +20,5 @@ code-clean                        personal
 commit-change                     personal
 
 # Session hygiene
-checkpoint
+context-save
 land-and-deploy

lib/profiles/full.profile

@@ -35,7 +35,7 @@ commit-change                     personal
 # === Ship + review + land ============================================
 ship
 review
-checkpoint
+context-save
 land-and-deploy
 setup-deploy
 

lib/profiles/web-full.profile

@@ -26,7 +26,7 @@ hotfix                            personal
 bugfix                            personal
 ship
 review
-checkpoint
+context-save
 commit-change                     personal
 refactor                          personal
 

lib/profiles/web.profile

@@ -25,7 +25,7 @@ ship-feature                      personal
 hotfix                            personal
 ship                                                # gstack
 review                                              # gstack
-checkpoint                                          # gstack
+context-save                                        # gstack
 commit-change                     personal
 refactor                          personal