feat: AI inline assistant for SQL editor

[datlechin]

Summary

Adds an inline AI assistant to the main SQL editor (PR F from docs/refactor/ai-chat-redesign.md).

• Select SQL in the editor and press Ctrl+Return (or pick Rewrite with AI... from the right-click menu) to open a floating prompt strip anchored above the selection.
• Type the change you want and press Return to stream the rewrite. The proposed text streams in below the prompt as a diff: the original selection is shown red with a strikethrough, the proposed replacement in green.
• Accept with Cmd+Return to replace the selection in place via the editor's existing edit pipeline. Reject with Esc to dismiss.

Architecture

• InlineAssistantSession (@Observable @MainActor) drives request → streamed response. Reuses AIProviderFactory.resolve(...) and ChatTransport.streamChat(...); no duplicated streaming logic.
• AIPromptTemplates+Rewrite adds the system + user prompts for rewrite-in-place. Schema context is included when the user has it enabled in AI settings.
• InlineAssistantPromptView is a SwiftUI view: text field, action buttons, and a streamed diff with monospaced strikethrough red / green tinting.
• InlineAssistantOverlayController hosts the view in a borderless NSPanel child window anchored to the editor selection rect via textView.layoutManager.rectForOffset(...). The panel repositions on parent move/resize and clamps to the visible screen.
• InlineAssistantPresenter owns the lifecycle inside the editor coordinator: builds the session, presents the overlay, applies the replacement on accept, and dismisses on reject/cancel.
• SQLEditorCoordinator installs the presenter and a per-editor NSEvent.addLocalMonitorForEvents for Ctrl+Return. The monitor fires only when the editor is first responder, has a non-empty selection, and AI is enabled. The existing EditorEventRouter is untouched.

Test plan

• Build the app, configure an AI provider in Settings > AI.
• Open a SQL editor tab, select a query fragment, press Ctrl+Return. Confirm the prompt strip appears anchored above the selection.
• Type a change ("rename users to people"), press Return, watch the diff stream in. Confirm strikethrough on the original and green proposed text.
• Press Cmd+Return to accept. Confirm the selection is replaced in place and undo (Cmd+Z) reverts it.
• Repeat and press Esc to reject. Confirm no edit and the panel closes.
• Right-click a selection, pick Rewrite with AI.... Confirm same flow as the keyboard shortcut.
• With no selection, press Ctrl+Return. Confirm beep and no panel (Ctrl+Return passes through to default text view behavior when nothing is selected).
• Resize/move the editor window with the panel open. Confirm the panel re-anchors.
• Disable AI in settings. Confirm Ctrl+Return no longer triggers the assistant.

References

• Roadmap row: docs/refactor/ai-chat-redesign.md PR F.
• New shortcut: docs/features/keyboard-shortcuts.mdx and docs/features/ai-assistant.mdx.

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