Release secrets-mcp 0.3.0: folder/type schema and MCP folder disambiguation

- Rename namespace/kind to folder/type on entries, audit_log, and history tables;
  add notes. Unique key is (user_id, folder, name).
- Service layer and MCP tools support name-first lookup with optional folder when
  multiple entries share the same name.
- secrets_delete dry_run uses the same disambiguation as real deletes.
- Add scripts/migrate-v0.3.0.sql for manual DB migration. Refresh README and
  AGENTS.md.

Made-with: Cursor

crates/secrets-core/src/service/env_map.rs

@@ -12,8 +12,8 @@ use crate::service::search::{fetch_entries, fetch_secrets_for_entries};
 #[allow(clippy::too_many_arguments)]
 pub async fn build_env_map(
     pool: &PgPool,
-    namespace: Option<&str>,
-    kind: Option<&str>,
+    folder: Option<&str>,
+    entry_type: Option<&str>,
     name: Option<&str>,
     tags: &[String],
     only_fields: &[String],
@@ -21,7 +21,7 @@ pub async fn build_env_map(
     master_key: &[u8; 32],
     user_id: Option<Uuid>,
 ) -> Result<HashMap<String, String>> {
-    let entries = fetch_entries(pool, namespace, kind, name, tags, None, user_id).await?;
+    let entries = fetch_entries(pool, folder, entry_type, name, tags, None, user_id).await?;
 
     let mut combined: HashMap<String, String> = HashMap::new();
 
@@ -68,16 +68,8 @@ async fn build_entry_env_map(
 
     // Resolve key_ref
     if let Some(key_ref) = entry.metadata.get("key_ref").and_then(|v| v.as_str()) {
-        let key_entries = fetch_entries(
-            pool,
-            Some(&entry.namespace),
-            Some("key"),
-            Some(key_ref),
-            &[],
-            None,
-            None,
-        )
-        .await?;
+        let key_entries =
+            fetch_entries(pool, None, Some("key"), Some(key_ref), &[], None, None).await?;
 
         if let Some(key_entry) = key_entries.first() {
             let key_ids = vec![key_entry.id];