[FabioHAraujo]

Closes #8

Problem and resulting behavior

The sidebar only had a small ⋯ menu on connections. Schemas, databases and objects had no actions, so dropping a table, reading its DDL, renaming it or creating a new one meant writing the SQL by hand.

Now a right-click (or the context-menu key, or the ⋯ button shown on hover) opens a menu for every node of the tree, with what makes sense for that node and engine:

• Connection: new query, connect, refresh, disconnect, create schema (Oracle: a user template) or database, server sessions, show a SQLite file in its folder, edit, duplicate, copy details, delete.
• Schema / database: new query working in it, refresh, create table (designer), view/function/procedure/sequence templates, rename (PostgreSQL), copy name, drop (type the name to confirm; CASCADE where supported), Redis FLUSHDB.
• Tables and other objects: select, count, Show DDL, generate SELECT/INSERT/UPDATE/DELETE/CREATE INDEX, edit table (designer → per-engine ALTER TABLE), rename, duplicate with or without rows, empty, refresh materialized views, copy names and column lists, drop any kind of object. Redis keys: show, TTL, rename, expire, persist, delete.

Every change shows its SQL before running (on the tree's own session, never a tab's) and can open in the editor instead.

Backend: a new object_ddl command reads DDL from each database's catalog (pg_get_*def + catalog, DBMS_METADATA, SHOW CREATE, OBJECT_DEFINITION + sys.*, sqlite_schema), and list_columns now reports column defaults.

Validation

• src/lib/sql/ddl.fixtures.json holds the statements ddl.ts writes for a full scenario per dialect (create, index, foreign key, designer ALTERs, rename, duplicate, truncate, drop, schemas, primary key added later). drivers/ddl_fixtures.rs runs it on PostgreSQL 13 and 17, Oracle 23ai and XE 21c, MySQL 8.4, MariaDB 11.4, SQL Server 2022 and SQLite in CI, plus a DDL round trip for tables, views and sequences (read the DDL, drop the object, run the DDL, compare the columns) and a DDL check for functions.
• bun test (unit tests for ddl.ts, including that the editor's script splitter keeps PL/SQL and T-SQL blocks whole), svelte-check, cargo clippy -D warnings, cargo fmt.
• Menus, dialogs and the designer checked in the browser with the development mock, and in a debug build of the Tauri app (embedded assets) against a real SQLite file: Show DDL, designer rename + add column, duplicate with rows, count, empty, drop view, drop table with typed confirmation.

Additional context

• Export and import are tracked separately in Export and import: tables, schemas and databases #16 (Export a table as a SQL script (structure only, or structure and data) #10–Copy tables between connections, across engines #15).
• What an engine cannot do is explained instead of attempted: SQLite type/NULL/default changes, replacing an existing PostgreSQL/SQL Server primary key (the constraint name is in the DDL).