### What problem does this PR solve?
Closes#15611.
RAGFlow's fallback reasoning parser only recognized the exact model
family `qwen3`. For provider-prefixed Qwen model names such as
SiliconFlow's `qwen/qwen3-8b`, the derived model class can be
`qwen/qwen3`, so inline `<think>...</think>` content was not split from
the visible answer when `reasoning_content` was absent.
This PR normalizes model-family detection before fallback reasoning
extraction, keeps the parser nil-safe, and adds focused tests for Qwen3
variants plus Gitee and SiliconFlow chat responses.
It also makes SiliconFlow propagate `ChatConfig.Thinking` into the chat
request body, matching the existing Gitee behavior, so Qwen thinking
mode is actually enabled when requested.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] Refactoring
### Validation
- `/root/go/bin/gofmt -l internal/entity/models/common.go
internal/entity/models/common_test.go
internal/entity/models/reasoning_family_provider_test.go
internal/entity/models/siliconflow.go`
- `git diff --check`
- `/root/go/bin/go test ./internal/entity/models -run
'Test(NormalizeModelFamily|GetThinkingAndAnswer|GiteeChatExtractsQwenThinkingFromInlineContent|SiliconflowChatExtractsProviderPrefixedQwenThinkingFromInlineContent)'
-vet=off -count=1`
Note: the full package command `/root/go/bin/go test
./internal/entity/models -vet=off -count=1` now runs locally, but it
currently fails on an unrelated existing
`TestAstraflowEmbedReturnsNoSuchMethod` panic in
`internal/entity/models/astraflow.go:482`.
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