docs: review and improve Phase 4 plan, fix PSAProvider reference in CLAUDE.md

Phase 4 plan corrections:
- Remove shadcn/ui from tech stack (not used in project)
- Replace shadcn Sheet with Tailwind slide-up panel for mobile modals
- Specify exact CSS variable names for custom branding overrides
- Add SEO crawlability note (deferred to Phase 5)

Phase 4 plan enhancements:
- Add notification retry mechanism with NotificationLog model + APScheduler
- Specify weasyprint for PDF export with Dockerfile deps
- Add "Copy to Clipboard" as primary export option
- Add Task 6.5: in-app notification center extending existing NotificationsPanel
- Specify slowapi for IP-based public endpoint rate limiting
- Add low-priority gallery analytics tracking section (PostHog events)

CLAUDE.md: fix BasePsaProvider → PSAProvider (matches actual class name)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -199,7 +199,7 @@ Official ConnectWise developer guides live in `docs/connectwise/best-practices/`
 
 - Auth: API Key auth (Base64 of `companyId+publicKey:privateKey`) + `clientId` header on every request
 - `clientId` is server-side config (`CW_CLIENT_ID` in `config.py`) — identifies the ResolutionFlow app, NOT per-tenant. Per-connection credentials: `company_id`, `public_key`, `private_key`, `server_url`
-- All PSA integration code in `services/psa/` — provider pattern with `BasePsaProvider` abstract class, `ConnectWiseProvider` implementation, `PsaProviderRegistry` for multi-PSA dispatch
+- All PSA integration code in `services/psa/` — provider pattern with `PSAProvider` abstract base class, `ConnectWiseProvider` implementation, `PsaProviderRegistry` for multi-PSA dispatch
 - PSA endpoints in `api/endpoints/psa_connections.py` — connection CRUD, ticket ops, member mapping
 - Credentials encrypted at rest via `services/psa/encryption.py` (Fernet)
 - Each MSP tenant provides their own CW credentials — ResolutionFlow stores these per-team, never per-user