chore: remove field_type and value_len from secrets schema

- Drop field_type, value_len from secrets and secrets_history tables
- Remove infer_field_type, compute_value_len from add.rs
- Simplify search output to field names only
- Update AGENTS.md, README.md documentation

Bump version to 0.9.4

Made-with: Cursor

src/models.rs

@@ -20,17 +20,11 @@ pub struct Entry {
 }
 
 /// A single encrypted field belonging to an Entry.
-/// field_name, field_type, and value_len are stored in plaintext so that
-/// `search` can show the schema without requiring the master key.
 #[derive(Debug, Serialize, Deserialize, sqlx::FromRow)]
 pub struct SecretField {
     pub id: Uuid,
     pub entry_id: Uuid,
     pub field_name: String,
-    /// Inferred type: "string", "number", "boolean", "json"
-    pub field_type: String,
-    /// Length of the plaintext value in characters (0 for binary-like PEM)
-    pub value_len: i32,
     /// AES-256-GCM ciphertext: nonce(12B) || ciphertext+tag
     pub encrypted: Vec<u8>,
     pub version: i64,
@@ -54,8 +48,6 @@ pub struct EntryRow {
 pub struct SecretFieldRow {
     pub id: Uuid,
     pub field_name: String,
-    pub field_type: String,
-    pub value_len: i32,
     pub encrypted: Vec<u8>,
 }