Cleanup warnings, add zcash_protocol dep, extract db bootstrap into submodule

- Remove dead Config fields (smtp_host, smtp_user) and unused SessionRequest.expires_at
- Switch scanner decrypt to non-deprecated zcash_protocol::consensus::NetworkType
- Add direct zcash_protocol = "0.7" dependency (matches zcash_address 0.10.1 graph)
- Extract schema migration tracking into db/schema_tracking.rs
- Move inline bootstrap migration into db/bootstrap.rs, reducing db.rs to 68 lines

Author: Kenbak

Cargo.lock

@@ -33,6 +33,7 @@ zcash_primitives = { version = "0.25", default-features = false }
 zcash_note_encryption = "0.4"
 orchard = { version = "0.11", default-features = false, features = ["std"] }
 zcash_address = "0.10"
+zcash_protocol = "0.7"
 
 # Crypto / hashing
 sha2 = "0.10"

Cargo.toml

@@ -19,8 +19,6 @@ pub struct Config {
     pub allowed_origins: Vec<String>,
     pub cookie_domain: Option<String>,
     pub frontend_url: Option<String>,
-    pub smtp_host: Option<String>,
-    pub smtp_user: Option<String>,
     pub smtp_pass: Option<String>,
     pub smtp_from: Option<String>,
     pub fee_ufvk: Option<String>,
@@ -69,8 +67,6 @@ impl Config {
                 .collect(),
             cookie_domain: env::var("COOKIE_DOMAIN").ok().filter(|s| !s.is_empty()),
             frontend_url: env::var("FRONTEND_URL").ok().filter(|s| !s.is_empty()),
-            smtp_host: env::var("SMTP_HOST").ok().filter(|s| !s.is_empty()),
-            smtp_user: env::var("SMTP_USER").ok().filter(|s| !s.is_empty()),
             smtp_pass: env::var("SMTP_PASS").ok().filter(|s| !s.is_empty()),
             smtp_from: env::var("SMTP_FROM").ok().filter(|s| !s.is_empty()),
             fee_ufvk: env::var("FEE_UFVK").ok().filter(|s| !s.is_empty()),