SQL-S4 — SQLite Sidebar tree integration

[ZhuchkaTriplesix]

Epic: #194
Depends on: #199 (SQL-S2), #200 (SQL-S3)
Source: docs/planned-0.4.5.md

Goal

Render SQLite connections and their schema nodes (Tables, Views, Indexes) in the sidebar connection tree (ConnectionsPanel).

Files

• lib/features/connections/widgets/connections_panel.dart (edit)
• lib/features/connections/widgets/sqlite_tree_node.dart (new)

Implementation

• Register SQLite connection type in the sidebar UI.
• Map connection schema output to folder-style tree nodes: "Tables", "Views", "Indexes".
• Render SQLite icon (or database icon) for SQLite connections.
• Enable expand/collapse on SQLite schema nodes.

Acceptance Criteria

• SQLite connection appears in the connections sidebar.
• Schema elements are correctly hierarchical (Tables -> Columns, Views, Indexes).
• Tree view handles schema updates/reloads seamlessly.
• Code is clean and passes flutter analyze.