fix(tls): honor Go key exchange defaults across transports

Remove the eight explicit curve overrides so Go 1.27 honors tlsmlkem=0
across Server listeners, node links and outbound transports. Remove the
unused shared curve option and add wire-level regression coverage.

Document CA trust and TLS upgrade behavior, retain the investigation
artifacts, and exclude their synthetic routes from the rebrand guard.
The product compatibility baseline remains unchanged.

Validation: focused race tests, HTTP tests, lint, compatibility guard
positive/negative controls, and a fresh Linux build with three isolated
OIDC integration scenarios all pass.

Adversarial review: Claude Code Fable 5.1, max effort.
Final verdict: APPROVE FOR COMMIT.

Signed-off-by: Feng Ruohang <rh@vonng.com>

buildscripts/rebrand-guard/main.go

@@ -115,7 +115,9 @@ func collect(repo string) (manifest, error) {
 	fset := token.NewFileSet()
 
 	for _, rel := range files {
+		// Investigation artifacts contain synthetic routes and archived configurations.
 		if rel == "SILO_REBRANDING_MIGRATION.md" ||
+			strings.HasPrefix(rel, "docs/investigations/") ||
 			strings.HasPrefix(rel, "buildscripts/rebrand-guard/") ||
 			strings.HasPrefix(rel, "buildscripts/helm-migration-guard/") {
 			continue