feat: add logic_level and primary_use metadata to model groups

Schema: Added logic_level (INTEGER) and primary_use (TEXT) columns
to model_groups table with auto-migration for existing databases.

Seed: Three new default groups:
  heavy-logic  (level 9) — Complex Coding, Logic, Agents
  standard-pro (level 5) — General Assistant, Long Docs
  fast-flow    (level 2) — Classification, JSON, Basic Q&A

Admin API: INSERT/UPDATE handlers now accept and persist the new fields.
Dashboard: Table shows Level and Primary Use columns; form includes
both fields with appropriate inputs and placeholders.

internal/db/db.go

@@ -130,6 +130,8 @@ func (db *DB) RunMigrations() error {
             targets TEXT NOT NULL DEFAULT '[]',
             complexity_threshold INTEGER,
             heuristic_rules TEXT,
+            logic_level INTEGER,
+            primary_use TEXT,
             created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
             updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
         )`,
@@ -162,6 +164,10 @@ func (db *DB) RunMigrations() error {
 		}
 	}
 
+	// Add columns to existing model_groups tables (safe — SQLite ignores duplicates on error)
+	db.Exec("ALTER TABLE model_groups ADD COLUMN logic_level INTEGER")
+	db.Exec("ALTER TABLE model_groups ADD COLUMN primary_use TEXT")
+
 	// Default admin user
 	var count int
 	if err := db.Get(&count, "SELECT COUNT(*) FROM users"); err != nil {
@@ -190,14 +196,19 @@ func (db *DB) RunMigrations() error {
 	// Seed default model groups
 	defaultGroups := []struct {
 		id, strategy, targets string
+		logicLevel *int
+		primaryUse *string
 	}{
-		{"deepseek-auto", "heuristic", `["deepseek-chat","deepseek-reasoner"]`},
-		{"openai-auto", "heuristic", `["gpt-4o-mini","gpt-4o"]`},
-		{"gemini-auto", "heuristic", `["gemini-2.0-flash","gemini-2.5-pro"]`},
+		{"deepseek-auto", "heuristic", `["deepseek-chat","deepseek-reasoner"]`, nil, nil},
+		{"openai-auto", "heuristic", `["gpt-4o-mini","gpt-4o"]`, nil, nil},
+		{"gemini-auto", "heuristic", `["gemini-2.0-flash","gemini-2.5-pro"]`, nil, nil},
+		{"heavy-logic", "heuristic", `["grok-4.3","kimi-k2.5","deepseek-v4-pro"]`, intPtr(9), strPtr("Complex Coding, Logic, Agents.")},
+		{"standard-pro", "heuristic", `["gpt-5.4-mini","gemini-3-flash"]`, intPtr(5), strPtr("General Assistant, Long Docs.")},
+		{"fast-flow", "heuristic", `["deepseek-v4-flash","gpt-5.4-nano"]`, intPtr(2), strPtr("Classification, JSON, Basic Q&A.")},
 	}
 	for _, g := range defaultGroups {
-		db.Exec(`INSERT OR IGNORE INTO model_groups (id, strategy, targets) VALUES (?, ?, ?)`,
-			g.id, g.strategy, g.targets)
+		db.Exec(`INSERT OR IGNORE INTO model_groups (id, strategy, targets, logic_level, primary_use) VALUES (?, ?, ?, ?, ?)`,
+			g.id, g.strategy, g.targets, g.logicLevel, g.primaryUse)
 	}
 
 	return nil
@@ -293,6 +304,11 @@ type ModelGroup struct {
 	Targets             string    `db:"targets" json:"targets"` // JSON array
 	ComplexityThreshold *int      `db:"complexity_threshold" json:"complexity_threshold"`
 	HeuristicRules      *string   `db:"heuristic_rules" json:"heuristic_rules"`
+	LogicLevel          *int      `db:"logic_level" json:"logic_level"`
+	PrimaryUse          *string   `db:"primary_use" json:"primary_use"`
 	CreatedAt           time.Time `db:"created_at" json:"created_at"`
 	UpdatedAt           time.Time `db:"updated_at" json:"updated_at"`
 }
+
+func intPtr(v int) *int     { return &v }
+func strPtr(v string) *string { return &v }