fix(pii): resolve inconsistent PII detection for EMAIL_ADDRESS

[yehudit1987]

Fix critical PII detection inconsistency where EMAIL_ADDRESS was not
detected while US_SSN was correctly blocked. Root cause: the Rust FFI
only used TraditionalBertTokenClassifier without fallback to ModernBERT.

Changes:

Rust FFI (candle-binding/src/ffi/classify.rs):

• Add ModernBERT fallback when TraditionalBERT classifier unavailable
• Return explicit results with proper error messages per classifier type
• Let Go layer handle confidence threshold (configured at 0.7)

PII Policy (src/semantic-router/pkg/utils/pii/policy.go):

• Add BIO-tag prefix stripping (B-, I-, O-, E-) for flexible matching
• "ORGANIZATION" in config now matches "B-ORGANIZATION" from model
• Validate only known BIO prefixes for security

Response Headers (src/semantic-router/pkg/utils/http/response.go):

• Add x-vsr-pii-types header exposing detected PII types
• Improves debuggability when requests are blocked

Configuration (3 files):

• Allow ORGANIZATION type for biology queries (false positive fix)
• Allow GPE type for general knowledge queries (country names)

E2E Tests:

• Refactor plugin_chain_execution.go to load cases from JSON
• Add testdata/plugin_chain_cases.json with 23 comprehensive cases
• Cover EMAIL, SSN, phone numbers, clean queries, and edge cases

Fixes #712

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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:

📁 candle-binding

Owners: @rootfs
Files changed:

• candle-binding/src/ffi/classify.rs

📁 deploy

Owners: @rootfs, @Xunzhuo
Files changed:

• deploy/kubernetes/aibrix/semantic-router-values/values.yaml

📁 e2e

Owners: @Xunzhuo
Files changed:

• e2e/profiles/ai-gateway/profile.go
• e2e/profiles/ai-gateway/values.yaml
• e2e/profiles/aibrix/profile.go
• e2e/profiles/dynamic-config/crds/intelligentroute.yaml
• e2e/testcases/plugin_chain_execution.go
• e2e/testcases/testdata/plugin_chain_cases.json

📁 src

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

• src/semantic-router/pkg/headers/headers.go
• src/semantic-router/pkg/utils/http/response.go
• src/semantic-router/pkg/utils/pii/policy.go

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🎉 Thanks for your contributions!

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