Add param declaration storage and validation to engine index

Implements the ParamDeclaration slice of the primary index: DataValue::ParamDeclaration
holds a regex + named capture group + MetricPrimitiveKind, stored under
IndexKey::ParamDeclaration{name} between LogParamSplit and ParamMetricSplit.
EngineMessage gains DeclareParam (validates the regex compiles and the capture
group exists before storing, returning a clear error otherwise) and
RemoveParamDeclaration; EngineQuery gains ParamDeclarations to list them back out
as ParamDeclarationDto. No API wiring yet (separate ticket).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o

Cargo.lock

@@ -2,6 +2,15 @@
 # It is not intended for manual editing.
 version = 4
 
+[[package]]
+name = "aho-corasick"
+version = "1.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c982642fa9e8606056828ee9a8505737230110bb1099153c79efe865c59d12ba"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "anstream"
 version = "1.0.0"
@@ -414,6 +423,7 @@ version = "0.1.0"
 dependencies = [
  "axum",
  "clap",
+ "regex",
  "serde",
  "serde_json",
  "tokio",
@@ -482,6 +492,35 @@ dependencies = [
  "bitflags",
 ]
 
+[[package]]
+name = "regex"
+version = "1.13.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f020237b6c8eed93db2e2cb53c00c60a8e1bc73da7d073199a1180401450218d"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-automata",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-automata"
+version = "0.4.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ad8553b9b26413251cbf30e620595c7a41b3887f03da04579c0e6b0d6a06b4b2"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d6f6ff9a378485b298a5286656da665ba74413d36db0979633275d2e708145d4"
+
 [[package]]
 name = "ryu"
 version = "1.0.23"