chore(release): secrets-mcp 0.4.0

Bump version for the N:N entry_secrets data model and related MCP/Web
changes. Remove superseded SQL migration artifacts; rely on auto-migrate.
Add structured errors, taxonomy normalization, and web i18n helpers.

Made-with: Cursor

crates/secrets-core/Cargo.toml

@@ -10,6 +10,7 @@ path = "src/lib.rs"
 [dependencies]
 aes-gcm.workspace = true
 anyhow.workspace = true
+thiserror.workspace = true
 chrono.workspace = true
 rand.workspace = true
 serde.workspace = true