Fix dashboard wasm build and feature-gate mongodb for wasm compatibility

- Feature-gate mongodb in compliance-core (optional, default on) so wasm
  builds don't pull in tokio/mio via mongodb
- Use bson v2 directly for ObjectId types (wasm-compatible)
- Restructure dashboard infrastructure/mod.rs: server function modules
  always compiled (for RPC stubs), server-only modules cfg-gated
- Remove reqwest from dashboard web feature (not needed, data flows
  through server functions)
- Add .gitignore

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

compliance-core/Cargo.toml

@@ -6,6 +6,10 @@ edition = "2021"
 [lints]
 workspace = true
 
+[features]
+default = ["mongodb"]
+mongodb = ["dep:mongodb"]
+
 [dependencies]
 serde = { workspace = true }
 serde_json = { workspace = true }
@@ -15,4 +19,5 @@ sha2 = { workspace = true }
 hex = { workspace = true }
 uuid = { workspace = true }
 secrecy = { workspace = true }
-mongodb = { workspace = true }
+bson = "2"
+mongodb = { workspace = true, optional = true }