Formula and percentage calculations in guest messages

Problem Statement:

• Hosts cannot use short codes or formulas in guest messages to perform calculations
• There's no way to automatically calculate percentages of rental totals (e.g., 50% of booking amount)
• Hosts creating manual booking agreements need to specify payment schedules based on percentages (e.g., 50% due at booking, 50% due 60 days out)
• Security deposits cannot be automatically added to the first payment using calculations

Current Workaround:

• Hosts manually calculate percentages and payment amounts outside of Hospitable
• Hosts type out calculated amounts manually in guest messages
• This is time-consuming and error-prone, especially for complex payment schedules

Impact:

• Increased manual work for hosts managing payment schedules
• Risk of calculation errors in payment amounts
• More friction when creating booking agreements with guests

Proposed Solution:

• Add support for short codes or formula-like syntax in guest messages
• Allow percentage calculations (e.g., %total% * 0.5 for 50% of total)
• Enable mathematical operations similar to spreadsheet formulas

Unlock:

• Hosts can automatically calculate and display payment amounts in guest messages
• Payment schedules can be dynamically generated based on percentages of the rental total
• Security deposits and other fees can be automatically added to payment calculations
• Reduced manual work and fewer calculation errors