phsl / new-api

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