feat: support request_header key source

[seefs001]

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渠道亲和配置规则支持配置请求头

🚀 变更类型 / Type of change

• 🐛 Bug 修复 (Bug fix) - 请关联对应 Issue，避免将设计取舍、理解偏差或预期不一致直接归类为 bug
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• ⚡ 性能优化 / 重构 (Refactor)
• 📝 文档更新 (Documentation)

🔗 关联任务 / Related Issue

• Closes 基于 Header 作为 Key 的亲和性能力 #4896

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Summary by CodeRabbit

• New Features
  • Added support for a request_header key source for channel affinity, including UI support and updated validation; header values are trimmed when read.
• Tests
  • Added unit tests covering header extraction and affinity resolution based on request headers.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 601905dc-4201-4356-b20a-bcde58d782e6

📥 Commits

Reviewing files that changed from the base of the PR and between 755d497 and 21b28a6.

📒 Files selected for processing (2)

• web/default/src/features/system-settings/general/channel-affinity/rule-editor-dialog.tsx
• web/default/src/features/system-settings/general/channel-affinity/types.ts

✅ Files skipped from review due to trivial changes (1)

• web/default/src/features/system-settings/general/channel-affinity/rule-editor-dialog.tsx

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Walkthrough

This PR adds support for extracting channel affinity keys from HTTP request headers. The backend extracts and trims header values based on a configured key name, while the frontend UI allows users to select and configure header-based affinity rules with appropriate validation and guidance.

Changes

Request Header Channel Affinity

Layer / File(s)	Summary
Backend request header extraction and integration service/channel_affinity.go, service/channel_affinity_template_test.go	extractChannelAffinityValue reads headers from Gin context with nil/empty guards and trims whitespace. New unit test verifies extraction and trimming from X-Affinity-Key header. Integration test configures a ChannelAffinityRule with request_header source, caches the result, and validates GetPreferredChannelByAffinity returns the correct channel and context metadata.
Frontend channel affinity settings UI web/classic/src/pages/Setting/Operation/SettingsChannelAffinity.jsx, web/default/src/features/system-settings/general/channel-affinity/types.ts, web/default/src/features/system-settings/general/channel-affinity/rule-editor-dialog.tsx, setting/operation_setting/channel_affinity_setting.go	Settings form adds request_header to the selectable key source types. Validation logic accepts the new type alongside context-based types. Description text and input placeholder are updated to document header-based configuration and suggest X-Affinity-Key as the example header name. Client-side KeySource.type union includes 'request_header'.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

🐇 I nibble headers, soft and neat,
I trim the corners, make the key complete,
From X-Affinity-Key I gently peep,
Cached and guided, channels I keep,
A happy hop — affinity now talks sweet.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'feat: support request_header key source' clearly and concisely summarizes the main change—adding support for request headers as a key source for channel affinity.
Linked Issues check	✅ Passed	The PR successfully implements the core requirement from issue #4896: enabling HTTP request headers as a key source for channel affinity, with supporting tests and UI updates across both backend and frontend.
Out of Scope Changes check	✅ Passed	All changes are directly related to implementing the request_header key source feature, with no unrelated modifications detected in the backend logic, tests, or frontend components.

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