fix: address review feedback on PR #106

- Remove unused envOrDefaultBool function and its test (Sonnet #3266 NIT)
- Replace Unicode em dashes with ASCII in slog messages (GPT #3267 NIT)
- Add scheme validation for vcsURL before embedding in Markdown link
  (Security #3269 MINOR — defense-in-depth against unsafe schemes)
- Extract ReviewerSelfRequester interface to remove concrete gitea.Adapter
  dependency from main's self-reviewer path (Sonnet #3266 NIT)
- Add compile-time conformance assertion and test for Adapter.RequestReviewerSelf

vcs/interfaces.go

@@ -41,3 +41,11 @@ type Client interface {
 	Reviewer
 	Identity
 }
+
+// ReviewerSelfRequester is an optional interface implemented by adapters that support
+// requesting the authenticated user as a reviewer on a pull request. This is used for
+// Gitea-specific behavior (ensuring the bot appears in required-reviewer checks).
+// Consumers should use interface assertion: if sr, ok := client.(ReviewerSelfRequester); ok { ... }
+type ReviewerSelfRequester interface {
+	RequestReviewerSelf(ctx context.Context, owner, repo string, number int, user string) error
+}