fix: add remediations on EXT-2 DoS and Auth Failures

[Manuthor]

OWASP security hardening across the KMS server:

• EXT2-2/A03-2: TTLV binary parser recursion depth limit (MAX=64) + tests
• EXT2-3/A03-3: TTLV XML parser stack depth limit (MAX=64)
• EXT2-1/A04-1: HTTP payload limit 10GB -> 64MB (PayloadConfig + JsonConfig)
• EXT2-5/A04-2: Rate-limiting via actix-governor (KMS_RATE_LIMIT_PER_SECOND config)
• A05-1/A01-1: Replace Cors::permissive() on KMIP default scope with Cors::default()
• A07-1: JWT algorithm confusion fix: asymmetric-only allowlist + explicit validation.algorithms
• A07-2: API token constant-time comparison via subtle::ConstantTimeEq
• A09-1: DB URL password masking in Display impl (mask_db_url_password helper)
• A09-2: TLS P12 password proper [****] redaction
• Update audit script CORS check for enterprise-integration scopes

cargo clippy-all: clean
cargo test-non-fips: 0 failures
audit.sh: 8 PASS, 8 WARN, 0 FAIL