feat: add system prompt toggle endpoint

[rootfs]

What type of PR is this?

Add an endpoint to set system prompt injection to allow runtime management. This endpoint is only turned on with explicit command line option

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Release Notes: Yes/No

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[github-actions]

👥 vLLM Semantic Team Notification

The following members have been identified for the changed files in this PR and have been automatically assigned:

📁 src

Owners: @rootfs, @Xunzhuo, @wangchen615
Files changed:

• src/semantic-router/cmd/main.go
• src/semantic-router/pkg/api/server.go
• src/semantic-router/pkg/api/server_test.go
• src/semantic-router/pkg/config/config.go
• src/semantic-router/pkg/extproc/request_handler.go
• src/semantic-router/pkg/services/classification.go

📁 tools

Owners: @yuluo-yx, @rootfs, @Xunzhuo
Files changed:

• tools/make/build-run-test.mk

📁 website

Owners: @Xunzhuo
Files changed:

• website/docs/overview/categories/configuration.md

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🎉 Thanks for your contributions!

This comment was automatically generated based on the OWNER files in the repository.

[Copilot]

Pull Request Overview

Adds runtime management of category-specific system prompts, including enable/disable and injection mode control, exposed via optional API endpoints.

• Introduces system prompt configuration endpoints guarded by a CLI flag.
• Adds per-category enable flag and injection mode ("replace" vs "insert") and modifies injection logic accordingly.
• Adds tests for endpoint security and functionality plus CLI integration.

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/semantic-router/pkg/services/classification.go	Adds getters/setters to expose and update router config at runtime.
src/semantic-router/pkg/extproc/request_handler.go	Adds injection mode support and switches to using live global config; adds extensive logging.
src/semantic-router/pkg/config/config.go	Adds category-level system prompt enable flag, mode handling, and lookup helpers.
src/semantic-router/pkg/api/server.go	Adds flag-controlled system prompt management endpoints and handlers.
src/semantic-router/pkg/api/server_test.go	Introduces tests for security gating and functional updates of system prompt settings.
src/semantic-router/cmd/main.go	Adds CLI flag and passes it into server startup.

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[rootfs]

merging it for now, need it for next PR.

[Xunzhuo]

overall LGTM