🐛 fix(ability): prevent duplicate (group, model) pairs when saving channels

When importing large model lists (≈700+) an attempt to save a channel
could fail with:

    Error 1062 (23000): Duplicate entry 'default-DeepSeek-1' for key 'abilities.PRIMARY'

Root cause: AddAbilities / UpdateAbilities inserted the same
(group, model) pair multiple times if the input list contained
duplicates or case-variants (e.g. `default` vs `Default`).

Changes:
• ability.go
  – AddAbilities: introduced `abilitySet` to deduplicate by
    lower-cased `group|model` key before batch-inserting.
  – UpdateAbilities: applied the same deduplication logic when
    rebuilding abilities inside a transaction.

Notes:
• The lower-casing is only for set comparison; the original
  `group` and `model` values are preserved when persisting to DB,
  so case sensitivity of stored data is unchanged.
• Batch chunking logic (lo.Chunk) and performance characteristics
  remain unaffected.

Fixes #1215

model/ability.go

@@ -133,9 +133,15 @@ func GetRandomSatisfiedChannel(group string, model string, retry int) (*Channel,
 func (channel *Channel) AddAbilities() error {
 	models_ := strings.Split(channel.Models, ",")
 	groups_ := strings.Split(channel.Group, ",")
+	abilitySet := make(map[string]struct{})
 	abilities := make([]Ability, 0, len(models_))
 	for _, model := range models_ {
 		for _, group := range groups_ {
+			key := strings.ToLower(group) + "|" + strings.ToLower(model)
+			if _, exists := abilitySet[key]; exists {
+				continue
+			}
+			abilitySet[key] = struct{}{}
 			ability := Ability{
 				Group:     group,
 				Model:     model,
@@ -194,9 +200,15 @@ func (channel *Channel) UpdateAbilities(tx *gorm.DB) error {
 	// Then add new abilities
 	models_ := strings.Split(channel.Models, ",")
 	groups_ := strings.Split(channel.Group, ",")
+	abilitySet := make(map[string]struct{})
 	abilities := make([]Ability, 0, len(models_))
 	for _, model := range models_ {
 		for _, group := range groups_ {
+			key := strings.ToLower(group) + "|" + strings.ToLower(model)
+			if _, exists := abilitySet[key]; exists {
+				continue
+			}
+			abilitySet[key] = struct{}{}
 			ability := Ability{
 				Group:     group,
 				Model:     model,