[FEATURE] Expenses module

[EdiWeeks]

Problem Statement

Thyme currently tracks time against projects/tasks and syncs to Business Central, but there is no way to record expenses. Users need to log expenses (e.g. travel, materials, subsistence) within Thyme so they can be captured against the relevant project and synced to Business Central alongside time entries.

Proposed Solution

Add an Expenses module to Thyme that lets users:

• Log an expense with the relevant details (amount, currency, date, category, project/task, description, and optionally an attached receipt).
• Associate the expense with a project (and task where applicable), consistent with how time entries work today.
• Sync logged expenses to Business Central so they appear against the project in the ERP.

Alternatives Considered

• Logging expenses directly in Business Central — rejected because it splits the user workflow across two systems and loses the unified project view Thyme provides.

Additional Context

• Should follow the existing BC integration patterns in src/services/bc/bcClient.ts.
• Open questions to refine during scoping: which BC entity expenses map to, expense categories/GL accounts, receipt attachment storage, and approval workflow (if any).