feat(matching): add an opt-in regex keyword matching mode

Fuzzy matching compares each keyword with every word of the commit
message. A word matches if it contains the keyword's letters in order.
Thus "feat" matches "fix(delegation):" and "major" matches
"deps(majors):", which gives false minor and major versions.

The new top-level config key "matching" accepts "fuzzy" (the default)
or "regex". In regex mode every wording keyword is a Go regular
expression. The tool compiles all of them when it loads the config and
runs them against the full commit message, so "(?m)^" anchors a
pattern to the start of a line. An invalid value, an invalid pattern,
or any other config parse error in regex mode stops the tool with a
non-zero exit code. It never falls back to fuzzy matching.

Fuzzy mode does not change. The blacklist check moves into one helper
that both modes use. A replay of 15 repositories gives the same
versions as before. This change improves version precision for the
repositories that opt in.

Claude-Session: https://claude.ai/code/session_01Qq1gbqQek1Zjtofo4VDRdW

cmd/main.go

@@ -18,6 +18,7 @@ limitations under the License.
 package cmd
 
 import (
+	"errors"
 	"fmt"
 	"os"
 
@@ -96,6 +97,15 @@ func main() {
 		// Read configuration
 		config, err := utils.ReadConfig(repo.LocalConfigFile)
 		if err != nil {
+			// A bad "matching" value or an invalid regex keyword is a real
+			// misconfiguration, not a missing-file situation: fail loudly
+			// instead of silently falling back to fuzzy matching.
+			if errors.Is(err, utils.ErrInvalidMatchingConfig) {
+				utils.Critical("Invalid matching configuration", map[string]interface{}{
+					"error": err.Error(),
+				})
+				os.Exit(1)
+			}
 			utils.Error("Unable to find config file. Using defaults and flags.", map[string]interface{}{
 				"file": repo.LocalConfigFile,
 			})
@@ -140,6 +150,7 @@ func main() {
 			repo.GitRepo.Commits,
 			repo.GitRepo.Tags,
 			repo.Config.Wording,
+			repo.Config.Matcher,
 			repo.Config.Blacklist,
 			repo.Semver,
 			params.varExisting || repo.Config.Force.Existing,