Add 52-week planting calendar with month fallback

Add indoor_sowing_weeks, direct_sowing_weeks, transplanting_weeks,
glasshouse_weeks, harvesting_weeks (integer[]) to backend Cultivar and
CreateCultivar structs with INSERT/UPDATE SQL bindings.

Frontend PlantingCalendar component rewritten as a compact 52-column
Gantt-style grid grouped by month headers. Prefers week data when
available, falls back to expanding month data into week ranges.
Calendar displayed full-width on cultivar detail page with color legend.

herbapi-api/src/db/models.rs

@@ -250,6 +250,11 @@ pub struct Cultivar {
     pub transplanting_months: Option<Vec<i32>>,
     pub glasshouse_months: Option<Vec<i32>>,
     pub harvesting_months: Option<Vec<i32>>,
+    pub indoor_sowing_weeks: Option<Vec<i32>>,
+    pub direct_sowing_weeks: Option<Vec<i32>>,
+    pub transplanting_weeks: Option<Vec<i32>>,
+    pub glasshouse_weeks: Option<Vec<i32>>,
+    pub harvesting_weeks: Option<Vec<i32>>,
     pub succession_planting_days: Option<i32>,
     pub planting_notes: Option<String>,
     pub propagation_methods: Option<Vec<String>>,
@@ -318,6 +323,11 @@ pub struct CreateCultivar {
     pub transplanting_months: Option<Vec<i32>>,
     pub glasshouse_months: Option<Vec<i32>>,
     pub harvesting_months: Option<Vec<i32>>,
+    pub indoor_sowing_weeks: Option<Vec<i32>>,
+    pub direct_sowing_weeks: Option<Vec<i32>>,
+    pub transplanting_weeks: Option<Vec<i32>>,
+    pub glasshouse_weeks: Option<Vec<i32>>,
+    pub harvesting_weeks: Option<Vec<i32>>,
     pub succession_planting_days: Option<i32>,
     pub planting_notes: Option<String>,
     pub propagation_methods: Option<Vec<String>>,