feat(filter): transport filter engine core — config, classification, SIMD evaluation

Chunk 1 of transport filter engine implementation:

- FilterRule, FilterAction, TransportFilterTierConfig config types
- Tier classification via text pattern matching (regex, not AST walk)
  - Tier 1: has(), ==, !=, startsWith, endsWith, contains
  - Tier 2: compound CEL (detected by exclusion)
  - Tier 3: restricted functions (matches, exists, map, etc.)
- CompiledFilter with Tier 1 SIMD evaluation via sonic_rs::get_from_slice
  - Dotted paths supported (metadata.source splits to path array)
  - MsgPack payloads bypass filters (JSON-only SIMD extraction)
- TransportFilterEngine assembly with startup validation:
  - Tier gate enforcement (reject above enabled tier)
  - Ordering warnings (higher tier before lower tier)
  - Filter count warnings (>20 per direction)
- FilterMetrics counters (transport_filtered_total)
- 56 tests covering config, classification, evaluation, engine assembly

regex added to transport feature (required for Tier 1 classification).

Author: catinspace-au

Cargo.toml

@@ -96,7 +96,7 @@ config-reload = ["config", "parking_lot", "tokio", "tracing"]
 config-postgres = ["config", "sqlx", "tokio", "serde_json"]
 
 # Transport features
-transport = ["tokio", "serde_json", "rmp-serde", "chrono", "async-trait"]
+transport = ["tokio", "serde_json", "rmp-serde", "chrono", "async-trait", "regex"]
 transport-memory = ["transport"]
 transport-kafka = ["transport", "rdkafka", "regex", "tokio-util"]
 transport-grpc = ["transport", "dep:tonic", "dep:tonic-prost", "dep:prost", "dep:prost-types", "dep:tonic-prost-build", "dep:prost-build"]