test(02-05): add tier1/tier2 provider guardrail test

- TestTier1Count asserts exactly 12 Tier 1 providers loaded
- TestTier2Count asserts exactly 14 Tier 2 providers loaded
- TestAllPatternsCompile verifies every regex compiles under RE2
- TestAllProvidersHaveKeywords guards Aho-Corasick pre-filter
- TestTier1/Tier2ProviderNames lock in expected provider names

Locks Phase 2 coverage against silent regressions in Phase 3+.
Addresses PROV-01, PROV-02.

pkg/providers/tier12_test.go

@@ -0,0 +1,103 @@
+package providers
+
+import (
+	"regexp"
+	"testing"
+)
+
+// expectedTier1 lists all 12 Tier 1 Frontier provider names (PROV-01).
+var expectedTier1 = []string{
+	"openai", "anthropic", "google-ai", "vertex-ai", "aws-bedrock",
+	"azure-openai", "meta-ai", "xai", "cohere", "mistral",
+	"inflection", "ai21",
+}
+
+// expectedTier2 lists all 14 Tier 2 Inference Platform provider names (PROV-02).
+var expectedTier2 = []string{
+	"groq", "replicate", "anyscale", "together", "fireworks",
+	"baseten", "deepinfra", "lepton", "modal", "cerebrium",
+	"novita", "sambanova", "octoai", "friendli",
+}
+
+func TestTier1Count(t *testing.T) {
+	reg, err := NewRegistry()
+	if err != nil {
+		t.Fatalf("NewRegistry failed: %v", err)
+	}
+	stats := reg.Stats()
+	if got := stats.ByTier[1]; got != 12 {
+		t.Errorf("Tier 1 count = %d, want 12", got)
+	}
+}
+
+func TestTier2Count(t *testing.T) {
+	reg, err := NewRegistry()
+	if err != nil {
+		t.Fatalf("NewRegistry failed: %v", err)
+	}
+	stats := reg.Stats()
+	if got := stats.ByTier[2]; got != 14 {
+		t.Errorf("Tier 2 count = %d, want 14", got)
+	}
+}
+
+func TestAllPatternsCompile(t *testing.T) {
+	reg, err := NewRegistry()
+	if err != nil {
+		t.Fatalf("NewRegistry failed: %v", err)
+	}
+	for _, p := range reg.List() {
+		for i, pat := range p.Patterns {
+			if _, err := regexp.Compile(pat.Regex); err != nil {
+				t.Errorf("provider %q pattern[%d] regex %q failed to compile: %v",
+					p.Name, i, pat.Regex, err)
+			}
+		}
+	}
+}
+
+func TestAllProvidersHaveKeywords(t *testing.T) {
+	reg, err := NewRegistry()
+	if err != nil {
+		t.Fatalf("NewRegistry failed: %v", err)
+	}
+	for _, p := range reg.List() {
+		if len(p.Keywords) == 0 {
+			t.Errorf("provider %q has no keywords (breaks AC pre-filter)", p.Name)
+		}
+	}
+}
+
+func TestTier1ProviderNames(t *testing.T) {
+	reg, err := NewRegistry()
+	if err != nil {
+		t.Fatalf("NewRegistry failed: %v", err)
+	}
+	for _, name := range expectedTier1 {
+		p, ok := reg.Get(name)
+		if !ok {
+			t.Errorf("Tier 1 provider %q not found in registry", name)
+			continue
+		}
+		if p.Tier != 1 {
+			t.Errorf("provider %q tier = %d, want 1", name, p.Tier)
+		}
+	}
+}
+
+func TestTier2ProviderNames(t *testing.T) {
+	reg, err := NewRegistry()
+	if err != nil {
+		t.Fatalf("NewRegistry failed: %v", err)
+	}
+	for _, name := range expectedTier2 {
+		p, ok := reg.Get(name)
+		if !ok {
+			t.Errorf("Tier 2 provider %q not found in registry", name)
+			continue
+		}
+		if p.Tier != 2 {
+			t.Errorf("provider %q tier = %d, want 2", name, p.Tier)
+		}
+	}
+}