build: Add regex dependency for cross-reference parsing

The note_parser module requires regex for extracting "mentioned in" and
"closed by" patterns from GitLab system notes. The regex crate provides:

- LazyLock-compatible lazy compilation (Regex::new at first use)
- Named capture groups for clean field extraction
- Efficient iteration over all matches via captures_iter()

Version 1.x is the current stable release with good compile times.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Cargo.lock

@@ -1122,6 +1122,7 @@ dependencies = [
  "libc",
  "open",
  "rand",
+ "regex",
  "reqwest",
  "rusqlite",
  "serde",

Cargo.toml

@@ -46,6 +46,7 @@ sha2 = "0.10"
 flate2 = "1"
 chrono = { version = "0.4", features = ["serde"] }
 uuid = { version = "1", features = ["v4"] }
+regex = "1"
 
 [target.'cfg(unix)'.dependencies]
 libc = "0.2"