Add user profile / settings page

[grmbyrn]

Problem

There is no way for users to configure their name, business name,
currency, or tax/VAT number. These are required to produce professional
invoices, especially for EU-based freelancers.

Proposed Solution

Add a /settings page where users can manage their profile information
that appears on invoices.

Acceptance Criteria

• Settings page exists at /settings
• User can save: full name, business name, address, currency, VAT/tax number
• A UserProfile model (or fields on User) stores this in the DB
• Invoice PDF pulls from this profile for the "From" section

Labels

enhancement