Feature: AI SQL Query Assistant for database-sourced charts

[vytisbulkevicius]

Summary

Adds a natural-language SQL assistant panel to the Source → Import from database tab of the chart editor. Users describe the data they want in plain English and the AI generates a correctly structured, ready-to-run SQL query tailored to the active chart type and database schema.

Features

• Natural language to SQL — Users type a plain-English description and the AI generates a complete SQL query with a brief explanation of what it retrieves.
• Chart-type awareness — The query always returns the correct number and type of columns for the active chart (e.g. pie = 2 cols, scatter = 3 cols, etc.).
• Table awareness — Available tables and their columns are passed to the AI so it references real schema instead of guessing.
• Conversational refinement — Follow-up prompts modify the previously generated query rather than starting fresh. The last generated query is sent as context alongside the new prompt.
• Multi-provider support — Works with OpenAI (GPT-4), Google Gemini, and Anthropic Claude. The provider dropdown only shows providers with a configured API key.
• Suggestion chips — Each response includes 2–3 related query ideas as clickable chips that pre-fill and trigger the next generation.
• One-click apply — "Use This Query" injects the generated SQL directly into the CodeMirror editor.
• MySQL compatibility layer — Detects environments where wrapping a date column in a function inside a WHERE clause crashes the connection (e.g. Local by Flywheel). The AI is instructed to use safe direct comparisons (WHERE post_date < DATE_SUB(CURDATE(), INTERVAL 1 YEAR)) and a post-processor rewrites any unsafe patterns in the generated query as a safety net.
• Empty-result handling — When a valid WHERE clause matches 0 rows and MySQL drops the connection (a known Local by Flywheel quirk), the server pings the DB after the error to distinguish a query-specific drop from a real outage, and returns a friendly "No results found" message instead of a misleading connection error.

Files changed

File	Change
classes/Visualizer/Module/AI.php	New — AJAX handler, AI provider calls, SQL system prompt, MySQL rewriter
js/ai-sql-query.js	New — UI interactions, AJAX, CodeMirror injection
classes/Visualizer/Render/Layout.php	Added AI assistant panel inside _renderDbQuery()
classes/Visualizer/Module/Chart.php	Registered/enqueued new script, added nonce_sql to visualizerAI, improved empty-result and connection-drop detection in getQueryData()
js/frame.js	Added error: callback to DB query AJAX, improved error display, handle empty-result success response

Test plan

• Panel appears in Source tab only when at least one AI API key is configured
• Generating a query for a pie chart returns exactly 2 columns
• Follow-up prompt "rename the value column" modifies the existing query, not creates a new one
• Clicking "Use This Query" populates the CodeMirror SQL editor
• On a WHERE clause that matches 0 rows, "Show Results" shows "No results found" instead of a connection error
• Suggestion chips pre-fill the prompt and trigger generation

Closes https://github.com/Codeinwp/visualizer-pro/issues/549

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