Closes #895

With Claude

Fix DrawTool bugs, template field naming, and null advanced filters

This PR addresses several critical bugs in the DrawTool feature and adds support for null/not-null
filtering operations.

🐛 Bug Fixes

Backend (API/Backend/Draw/)

• aggregations.js: Fixed promise chain issue where response was sent but the promise continued
  executing, causing potential errors when history is empty
• filesutils.js:
  • Fixed field name validation to allow spaces, dashes, dots in addition to alphanumeric and
    underscores (previously was too restrictive)
  • Added SQL injection protection by escaping single quotes in property keys
  • Improved error handling for malformed filter formats with proper 400 status responses

Frontend (src/essence/Tools/Draw/)

• DrawTool_Files.js: Fixed DynamicExtent state not resetting properly when toggling files off, which
  prevented proper reload on next toggle. Now clears:
  • Truncation state
  • Last requested location
  • Last requested extent
• DrawTool_Shapes.js: Fixed blur event handler to properly read input value from DOM element
• DrawTool_Templater.js: Added null safety checks using optional chaining (?.) to prevent errors when
  templateObj is undefined

✨ New Features

Advanced Filtering

• Added "Is Null" and "Is Not Null" operators to the Draw Tool advanced filter system
• Automatically hides value input field when null operators are selected (they don't require a value)
• Includes appropriate icons and tooltips for the new operators
• Backend support for isnull and isnotnull SQL operations

Template Field Validation

• Added validation for template field names to ensure they only contain safe characters: [a-zA-Z0-9
  _-.]
• Displays clear error message when invalid characters are used
• Prevents potential issues with field name handling in filters and queries

🎨 UI Improvements

• dropy.css: Increased dropdown max-height from 20em to 24em for better visibility of filter options

📝 Files Changed

• API/Backend/Draw/routes/aggregations.js
• API/Backend/Draw/routes/filesutils.js
• src/essence/Tools/Draw/DrawTool_Files.js
• src/essence/Tools/Draw/DrawTool_Shapes.js
• src/essence/Tools/Draw/DrawTool_Templater.js
• src/external/Dropy/dropy.css