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.

providers/zhipu.toml

@@ -1,5 +1,5 @@
 # Zhipu AI (GLM) — https://open.bigmodel.cn
-# Models: 2
+# Models: 4
 
 [provider]
 id = "zhipu"
@@ -8,6 +8,20 @@ api_key_env = "ZHIPU_API_KEY"
 base_url = "https://open.bigmodel.cn/api/paas/v4"
 key_required = true
 
+[[models]]
+id = "glm-5.1"
+display_name = "GLM-5.1"
+tier = "frontier"
+context_window = 131072
+max_output_tokens = 16384
+input_cost_per_m = 0.95
+output_cost_per_m = 3.15
+supports_tools = true
+supports_vision = true
+supports_streaming = true
+supports_thinking = true
+aliases = ["glm", "glm-5.1-latest"]
+
 [[models]]
 id = "glm-5-20250605"
 display_name = "GLM-5"
@@ -33,3 +47,16 @@ supports_tools = true
 supports_vision = true
 supports_streaming = true
 aliases = []
+
+[[models]]
+id = "glm-4.7-flash"
+display_name = "GLM-4.7 Flash"
+tier = "fast"
+context_window = 207872
+max_output_tokens = 16384
+input_cost_per_m = 0.0
+output_cost_per_m = 0.0
+supports_tools = true
+supports_vision = false
+supports_streaming = true
+aliases = []