feat: Add Dynamic Auto-Resizing Text Editor

[Dhruv1797]

Fixes: #284
Add a dynamic Text Editor where text always fits inside a fixed canvas by auto-resizing as content grows. On finalize, the text should export as an image similar to other elements.

Here is the demo video of this feature:

textfit_editor.mp4

Summary by Sourcery

Add a dynamic text editor that auto-resizes content to fit a fixed canvas and exports the final text as an image

New Features:

• Introduce TextFitEditor component for entering and auto-scaling text to fill a predefined canvas
• Add a Text action button in the BottomActionMenu to launch the text editor and insert the rendered text as an image

[sourcery-ai]

Reviewer's Guide

Adds a new TextFitEditor widget for dynamic, auto-resizing text editing and integrates it into the image editor's BottomActionMenu, enabling users to insert text that always fits the canvas and export it as an image.

Sequence diagram for adding text via TextFitEditor

sequenceDiagram
    actor User
    participant "BottomActionMenu"
    participant "TextFitEditor"
    participant "imgLoader"
    User->>"BottomActionMenu": Tap 'Text' button
    "BottomActionMenu"->>"TextFitEditor": Open editor with canvas size
    User->>"TextFitEditor": Enter text, select options
    "TextFitEditor"->>"BottomActionMenu": Return exported image bytes
    "BottomActionMenu"->>"imgLoader": updateImage(bytes)
    "BottomActionMenu"->>"imgLoader": saveFinalizedImageBytes(bytes)
    "BottomActionMenu"->>User: Show updated canvas

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Class diagram for new TextFitEditor widget

classDiagram
    class TextFitEditor {
      +int width
      +int height
      +TextFitEditor(width, height)
    }
    class TextFitEditorState {
      -TextEditingController _controller
      -GlobalKey _repaintKey
      -Color _textColor
      -Color _backgroundColor
      -TextAlign _align
      -List<Color> _availableColors
      +initState()
      +build(context)
      +_calculateCanvas(screenSize)
      +_fitFontSize(text, maxW, maxH, align)
      +_export(canvasSize)
    }
    TextFitEditor o-- TextFitEditorState

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File-Level Changes

Change	Details	Files
Integrate TextFitEditor into the BottomActionMenu	Import TextFitEditor at the top of image_editor.dart Add a new 'Text' action button that navigates to TextFitEditor Receive and handle returned PNG bytes from TextFitEditor Update and finalize the image via imgLoader and trigger onSourceChanged	lib/view/image_editor.dart
Implement TextFitEditor UI and core text-resizing logic	Calculate a canvas size that preserves the given aspect ratio Implement a binary-search font-size fitting algorithm to ensure text always fits Build controls for text input, color selection, alignment, and background Capture the widget via RepaintBoundary and export it as PNG bytes	lib/view/text_fit_editor.dart

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#284	Implement a dynamic Text Editor where text always fits inside a fixed canvas by auto-resizing as content grows.	✅
#284	Enable exporting the finalized text as an image, similar to other elements.	✅

Possibly linked issues

• Add Dynamic Auto-Resizing Text Editor #284: The PR implements the dynamic auto-resizing text editor described in the issue, including text fitting and image export.
• Add Dynamic Auto-Resizing Text Editor #284: The PR adds a dynamic text editor that auto-resizes text to fit a canvas and exports it as an image, directly addressing the issue's requirements.
• Add Dynamic Auto-Resizing Text Editor #284: The PR implements the dynamic auto-resizing text editor, allowing text to fit within a canvas and export as an image.

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[sourcery-ai]

Hey there - I've reviewed your changes - here's some feedback:

• Dispose the TextEditingController in TextFitEditorState.dispose to avoid memory leaks.
• Wrap the editor UI in a SafeArea or handle keyboard insets so the text field and controls aren’t obscured by system UI or the keyboard.
• Consider extracting the font fitting binary‐search logic (_fitFontSize) into a separate utility to improve reusability and testability.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Dispose the TextEditingController in TextFitEditorState.dispose to avoid memory leaks.
- Wrap the editor UI in a SafeArea or handle keyboard insets so the text field and controls aren’t obscured by system UI or the keyboard.
- Consider extracting the font fitting binary‐search logic (_fitFontSize) into a separate utility to improve reusability and testability.

## Individual Comments

### Comment 1
<location> `lib/view/text_fit_editor.dart:79-83` </location>
<code_context>
+  }
+
+  Future<Uint8List?> _export(Size canvasSize) async {
+    final boundary = _repaintKey.currentContext?.findRenderObject()
+        as RenderRepaintBoundary?;
+    if (boundary == null) return null;
+    final pixelRatio = widget.width / canvasSize.width;
+    final ui.Image image = await boundary.toImage(pixelRatio: pixelRatio);
+    final ui.ByteData? data =
+        await image.toByteData(format: ui.ImageByteFormat.png);
</code_context>

<issue_to_address>
**issue (bug_risk):** Check for zero or negative pixelRatio before calling toImage.

A guard clause to ensure pixelRatio is positive will prevent runtime errors if canvasSize.width is zero or negative.
</issue_to_address>

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