feat: initialize ERP base platform (extracted from HMS)

- Stripped 11 business crates (health, ai, dialysis, plugins)
- Cleaned AppState, AppConfig, main.rs from business coupling
- Reduced migrations from 169 to 53 (base-only)
- Removed health_provider trait from erp-core
- Removed business integration tests
- Removed gateway rate limiting middleware
- Base capabilities: auth, RBAC, JWT, config, workflow, message, plugin, audit, crypto, RLS, multi-tenant

Cargo check: OK
Cargo test: OK

crates/erp-core/Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "erp-core"
+version.workspace = true
+edition.workspace = true
+
+[dependencies]
+tokio.workspace = true
+serde.workspace = true
+serde_json.workspace = true
+uuid.workspace = true
+chrono.workspace = true
+thiserror.workspace = true
+anyhow.workspace = true
+tracing.workspace = true
+axum.workspace = true
+sea-orm.workspace = true
+async-trait.workspace = true
+utoipa.workspace = true
+aes-gcm = "0.10"
+hmac = "0.12"
+sha2 = "0.10"
+base64 = "0.22"
+hex = "0.4"
+rand = "0.8"
+dashmap = "6"
+ammonia.workspace = true