feat(plugins): add TealTiger deterministic governance guardrail

[nagasatish007]

Adds TealTiger as a native guardrails plugin for Portkey Gateway. Implements three guardrail functions:

• PII Detection (beforeRequestHook / afterRequestHook) — scans prompts and responses for SSN, credit cards, emails, phone numbers, IBAN, and passport numbers using 40+ regex patterns
• Secret Detection (beforeRequestHook / afterRequestHook) — detects API keys (OpenAI, AWS, GitHub, Slack), JWTs, private keys, and generic credentials
• Cost Governance (beforeRequestHook) — estimates request cost and blocks if it exceeds configured per-request budget

All evaluation is deterministic (regex + policy rules) — no external API calls, no LLM in the governance path, under 2ms per check.

Closes #1688

Architecture

plugins/tealtiger/
├── manifest.json         # Plugin definition (3 guardrail functions)
├── piiDetection.ts       # PII scanning (SSN, CC, email, phone, IBAN, passport)
├── secretDetection.ts    # Secret/credential detection (7 pattern families)
└── costGovernance.ts     # Pre-dispatch cost estimation + budget enforcement

Key Design Decisions

• No external dependency — all patterns are inline regex, no tealtiger npm package required. The plugin is self-contained.
• Fail-open on error — if governance evaluation throws, the request passes through (safety default for a gateway)
• Structured return data — every verdict includes governanceDecision, reasonCodes, riskScore, and evaluationEngine for downstream observability
• No credentials required — the plugin runs entirely in-process with no API key needed

Testing

Each function can be tested with Portkey's standard plugin test setup:

• PII: pass text with 123-45-6789 → expect verdict: false
• Secret: pass text with sk-abcdefghij1234567890abcd → expect verdict: false
• Cost: pass very long prompt with maxCostPerRequest: 0.001 → expect verdict: false

[nagasatish007]

Hi @narengogi, please review . Thanks