feat(gear): add filter paper category and optional brew association

- Add migration to extend gear CHECK constraint with 'filter_paper'
  and add nullable filter_paper_id column to brews
- Add FilterPaper variant to GearCategory enum
- Add filter_paper_id to Brew, NewBrew, and BrewWithDetails
- Add filter_paper_id to TimelineBrewData

migrations/0011_add_filter_paper.sql

@@ -0,0 +1,22 @@
+-- Add 'filter_paper' gear category and optional filter_paper_id on brews.
+--
+-- SQLite does not support altering CHECK constraints, so we recreate the gear
+-- table with the updated constraint.
+
+CREATE TABLE gear_new (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    category TEXT NOT NULL CHECK (category IN ('grinder', 'brewer', 'filter_paper')),
+    make TEXT NOT NULL,
+    model TEXT NOT NULL,
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+INSERT INTO gear_new (id, category, make, model, created_at, updated_at)
+SELECT id, category, make, model, created_at, updated_at FROM gear;
+
+DROP TABLE gear;
+ALTER TABLE gear_new RENAME TO gear;
+CREATE INDEX idx_gear_category ON gear(category);
+
+ALTER TABLE brews ADD COLUMN filter_paper_id INTEGER REFERENCES gear(id) ON DELETE SET NULL;

src/domain/brews.rs

@@ -12,6 +12,7 @@ pub struct Brew {
     pub grinder_id: GearId,
     pub grind_setting: f64,
     pub brewer_id: GearId,
+    pub filter_paper_id: Option<GearId>,
     pub water_volume: i32,
     pub water_temp: f64,
     pub created_at: DateTime<Utc>,
@@ -28,6 +29,7 @@ pub struct BrewWithDetails {
     pub roaster_slug: String,
     pub grinder_name: String,
     pub brewer_name: String,
+    pub filter_paper_name: Option<String>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -37,6 +39,7 @@ pub struct NewBrew {
     pub grinder_id: GearId,
     pub grind_setting: f64,
     pub brewer_id: GearId,
+    pub filter_paper_id: Option<GearId>,
     pub water_volume: i32,
     pub water_temp: f64,
 }

src/domain/gear.rs

@@ -11,6 +11,8 @@ use super::listing::{SortDirection, SortKey};
 pub enum GearCategory {
     Grinder,
     Brewer,
+    #[serde(rename = "filter_paper")]
+    FilterPaper,
 }
 
 impl GearCategory {
@@ -18,6 +20,7 @@ impl GearCategory {
         match self {
             GearCategory::Grinder => "grinder",
             GearCategory::Brewer => "brewer",
+            GearCategory::FilterPaper => "filter_paper",
         }
     }
 
@@ -25,6 +28,7 @@ impl GearCategory {
         match self {
             GearCategory::Grinder => "Grinder",
             GearCategory::Brewer => "Brewer",
+            GearCategory::FilterPaper => "Filter Paper",
         }
     }
 }
@@ -36,6 +40,7 @@ impl FromStr for GearCategory {
         match s.to_lowercase().as_str() {
             "grinder" => Ok(GearCategory::Grinder),
             "brewer" => Ok(GearCategory::Brewer),
+            "filter_paper" => Ok(GearCategory::FilterPaper),
             _ => Err(()),
         }
     }

src/domain/timeline.rs

@@ -16,6 +16,7 @@ pub struct TimelineBrewData {
     pub bag_id: i64,
     pub grinder_id: i64,
     pub brewer_id: i64,
+    pub filter_paper_id: Option<i64>,
     pub coffee_weight: f64,
     pub grind_setting: f64,
     pub water_volume: i32,