feat(model-registry): add provider field to all entries

Add optional provider field (anthropic, openai, alibaba, github,
openrouter, opencode) as groundwork for F-WE-PDIV provider diversity
enforcement in auto-model selection.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

model-registry/airouter-qwen3.yaml

@@ -1,5 +1,6 @@
 name: airouter-qwen3
 endpoint: airouter-qwen3
+provider: alibaba
 scores:
   complexity: 8
   test_pass_rate: 7

model-registry/claude-haiku-4.yaml

@@ -1,5 +1,6 @@
 name: claude-haiku-4
 endpoint: claude-haiku-4
+provider: anthropic
 scores:
   complexity: 5
   test_pass_rate: 7

model-registry/claude-opus-4.yaml

@@ -1,5 +1,6 @@
 name: claude-opus-4
 endpoint: claude-opus-4
+provider: anthropic
 scores:
   complexity: 10
   test_pass_rate: 9

model-registry/claude-sonnet-4.yaml

@@ -1,5 +1,6 @@
 name: claude-sonnet-4
 endpoint: claude-sonnet-4
+provider: anthropic
 scores:
   complexity: 8
   test_pass_rate: 9

model-registry/github-models-gpt4o.yaml

@@ -1,5 +1,6 @@
 name: github-models-gpt4o
 endpoint: github-models-gpt4o
+provider: github
 scores:
   complexity: 8
   test_pass_rate: 8

model-registry/gpt-4o-openai.yaml

@@ -1,5 +1,6 @@
 name: gpt-4o-openai
 endpoint: gpt-4o-openai
+provider: openai
 scores:
   complexity: 8
   test_pass_rate: 8

model-registry/opencode-zen-sonnet.yaml

@@ -1,5 +1,6 @@
 name: opencode-zen-sonnet
 endpoint: opencode-zen-sonnet
+provider: opencode
 scores:
   complexity: 8
   test_pass_rate: 9

model-registry/openrouter-sonnet.yaml

@@ -1,5 +1,6 @@
 name: openrouter-sonnet
 endpoint: openrouter-sonnet
+provider: openrouter
 scores:
   complexity: 8
   test_pass_rate: 9

model-registry/qwen3-235b.yaml

@@ -1,5 +1,6 @@
 name: qwen3-235b
 endpoint: qwen3-235b-vllm
+provider: alibaba
 scores:
   complexity: 8
   test_pass_rate: 8