feat: add 2026 Q2 flagship models (#76)

Add latest flagships released in April 2026 that registry missed:
- deepseek: V4-Pro, V4-Flash (2026-04-24, 1M context)
- qwen: qwen3.6-max-preview (2026-04-20, 256K context)
- moonshot: kimi-k2.6 (2026-04-20, 256K context)
- zhipu: glm-5.1 (2026-04-08), glm-4.7-flash (free tier)

Update default aliases: deepseek -> v4-pro, kimi -> k2.6, glm -> 5.1.

aliases.toml

@@ -11,7 +11,7 @@
 
 # Chinese models — common short names not on the canonical model entries
 "ernie" = "ernie-4.5-8k"
-"moonshot" = "kimi-k2.5"
+"moonshot" = "kimi-k2.6"
 "minimax" = "MiniMax-M2.7"
 "minimax-highspeed" = "MiniMax-M2.7-highspeed"
 "doubao" = "doubao-seed-2-0-pro-260215"