feat(notify): release v1.8.0 — Slack/Teams/Google Chat/Telegram/webhook notifications

- Add internal/notify package: best-effort release notifications to Slack, Microsoft Teams, Google Chat, Telegram, and a generic JSON webhook; every target is independently opt-in and a failed notification never fails the release
- Add notify config section (slack_webhook_url, teams_webhook_url, google_chat_webhook_url, telegram_bot_token/telegram_chat_id, webhook_url) with matching env var fallbacks; 100% coverage plus FuzzMessagePayloads
- Wire notification sending into run() — fires after tag+push (including --no-release), skipped on --no-push/--no-commit since nothing was published yet
- Document the notify section in README, Hugo docs, and .releaser.yml template; update CLAUDE.md architecture/fuzzing tables
- Also commit the Apache License 2.0 docs-site footer link (docs/hugo.toml geekdocContentLicense), left uncommitted from a prior change

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/notify/telegram_test.go

@@ -0,0 +1,53 @@
+package notify
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+func TestSendTelegram(t *testing.T) {
+	var got telegramPayload
+	var path string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		path = r.URL.Path
+		json.NewDecoder(r.Body).Decode(&got) //nolint:errcheck
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer srv.Close()
+
+	orig := telegramAPIBase
+	telegramAPIBase = srv.URL
+	defer func() { telegramAPIBase = orig }()
+
+	if err := sendTelegram(context.Background(), "bot-token", "chat-1", Message{Version: "v1.2.3", Notes: "notes body"}); err != nil {
+		t.Fatalf("sendTelegram: %v", err)
+	}
+	if !strings.Contains(path, "bot-token") {
+		t.Errorf("path = %q, want to contain bot token", path)
+	}
+	if got.ChatID != "chat-1" {
+		t.Errorf("ChatID = %q, want chat-1", got.ChatID)
+	}
+	if !strings.Contains(got.Text, "v1.2.3") || !strings.Contains(got.Text, "notes body") {
+		t.Errorf("Text = %q", got.Text)
+	}
+}
+
+func TestSendTelegramError(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusBadRequest)
+	}))
+	defer srv.Close()
+
+	orig := telegramAPIBase
+	telegramAPIBase = srv.URL
+	defer func() { telegramAPIBase = orig }()
+
+	if err := sendTelegram(context.Background(), "bot-token", "chat-1", Message{Version: "v1.0.0"}); err == nil {
+		t.Fatal("expected error for 400 response")
+	}
+}