feat: Add NLP support for slash commands and improve receipt validation

[sezallagwal]

Closes #31

Changes

NLP Fallback for Slash Commands

• Added handleNLPCommand(): Implemented in app/src/utils/command_utils.ts.
• LLM Parsing: Unrecognized commands now fall through to LLM parsing instead of failing immediately.
• Usage: Commands like /receipt change currency to USD now function identically to mentioning the bot directly.

Enforce Minimum Receipt Items

• Conditional UI: Modified app/src/modals/editReceiptModal.ts to conditionally hide the "Remove Item" button.
• Logic: The button is now visible only when items.length > 1.
• Goal: Prevents users from accidentally creating invalid empty receipts.

Discoverability

• Help Update: Updated the help message in app/src/utils/command_utils.ts.
• Examples: Users are now shown natural language examples (e.g., /receipt change currency to USD) in the help output.

Files Changed

• app/src/utils/command_utils.ts: Added NLP fallback logic and updated help strings.
• app/src/modals/editReceiptModal.ts: Added conditional rendering for the remove item button.

Demo

Recording.2026-01-21.084741.mp4

[sezallagwal]

@khelli07 @ashbunnn Can you review this pr?