Phase 4 PRD + plan: customer-flow redesign (Figma alignment)

Adds the Phase 4 requirement docs that align the customer app with the new
HaloBestie Figma design dump.

- requirement/flow_customer.md: source-of-truth numbered flow (input)
- requirement/flow_customer.mermaid.md: 6 mermaid diagrams + Figma cross-ref
- requirement/phase4-customer-flow.md: PRD (15 functional sections)
- requirement/phase4-customer-flow-plan.md: 10-stage implementation plan
- .gitignore: exclude requirement/Figma.zip + extracted Figma/ folder

Resolved product decisions: no free trial (replaced by configurable
first-session discount), pricing has independent chat/call groups,
voice-call mode is chat-with-badge (mitra shares Meet link manually),
social login is server-driven via /api/shared/auth-providers, ESP tags
are info-only (not used for matching).

No code changes; implementation starts at plan stage 0 (design system).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -10,3 +10,8 @@ build/
 .flutter-plugins
 .flutter-plugins-dependencies
 bugreport-*.zip
+
+# Figma design dump (do not check in)
+requirement/Figma.zip
+requirement/Figma/
+requirement/figma/