Add offline merchant category suggestions

openspec/changes/monthly-expense-tracker-v1/specs/category-suggestion/spec.md

@@ -0,0 +1,23 @@
+## ADDED Requirements
+
+### Requirement: System suggests categories from merchant names
+The system SHALL support merchant-name-based category suggestion for expense entry while keeping all suggestion logic fully offline.
+
+#### Scenario: Known merchant resolves from deterministic rules
+- **WHEN** the user enters a merchant or shop name that matches a known merchant rule
+- **THEN** the system assigns the mapped category without needing model inference
+
+#### Scenario: Unknown merchant falls back to local model
+- **WHEN** the user enters a merchant or shop name that does not match a known merchant rule
+- **THEN** the system asks the local AI service for a category suggestion and returns the suggested category
+
+### Requirement: Ambiguous suggestions remain user-controlled
+The system SHALL keep the final saved category under user control for ambiguous or model-generated suggestions.
+
+#### Scenario: User confirms model suggestion before save
+- **WHEN** the category suggestion comes from model inference instead of a deterministic rule
+- **THEN** the user can review and confirm or change the category before the expense is saved
+
+#### Scenario: No cloud fallback is used
+- **WHEN** the local suggestion service is unavailable
+- **THEN** the system continues to allow manual category selection and does not send merchant data to a hosted provider