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/teams.go

@@ -0,0 +1,31 @@
+package notify
+
+import (
+	"context"
+	"fmt"
+)
+
+// teamsPayload is a Microsoft Teams "Incoming Webhook" O365 connector card
+// (MessageCard schema) — the format Teams webhook URLs still accept.
+type teamsPayload struct {
+	Type    string `json:"@type"`
+	Context string `json:"@context"`
+	Summary string `json:"summary"`
+	Title   string `json:"title"`
+	Text    string `json:"text"`
+}
+
+func newTeamsPayload(msg Message) teamsPayload {
+	title := fmt.Sprintf("Released %s", msg.Version)
+	return teamsPayload{
+		Type:    "MessageCard",
+		Context: "http://schema.org/extensions",
+		Summary: title,
+		Title:   title,
+		Text:    msg.Notes,
+	}
+}
+
+func sendTeams(ctx context.Context, webhookURL string, msg Message) error {
+	return postJSON(ctx, webhookURL, newTeamsPayload(msg))
+}