[Server] Add DNS rebinding protection feature with middleware

[chr-hertel]

Adding HTTP middleware for DNS middleware protection - following conformance requirements.

• need to review myself first

[Copilot]

Pull request overview

Adds a server-side HTTP middleware to mitigate DNS rebinding attacks by validating Host and Origin headers against an allowlist, and wires it into the conformance test server to satisfy the conformance suite requirement.

Changes:

• Introduces DnsRebindingProtectionMiddleware for Host/Origin allowlist validation (defaulting to localhost variants).
• Adds unit tests covering allow/deny behavior, case-insensitivity, and custom allowlists.
• Enables the middleware in the conformance server and updates docs/changelog accordingly.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/Server/Transport/Http/Middleware/DnsRebindingProtectionMiddleware.php	Implements DNS rebinding protection by rejecting non-allowed Host/Origin.
tests/Unit/Server/Transport/Http/Middleware/DnsRebindingProtectionMiddlewareTest.php	Unit tests for middleware allow/deny and ordering behavior.
tests/Conformance/server.php	Adds the new middleware to the conformance server transport pipeline.
tests/Conformance/conformance-baseline.yml	Removes the DNS rebinding protection item from the baseline list.
docs/transports.md	Documents how to enable/configure the DNS rebinding middleware.
CHANGELOG.md	Notes the addition of DnsRebindingProtectionMiddleware.

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