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>

docs/content/changelog.md

@@ -3,6 +3,12 @@ title: Changelog
 weight: 50
 ---
 
+## v1.8.0 — 2026-07-12
+
+### Added
+
+- **Release notifications** — best-effort notification on release to Slack, Microsoft Teams, Google Chat, Telegram, and/or a generic JSON webhook via the new `notify` config section; every target is independently opt-in (config file or env var), and a failed notification never fails the release
+
 ## v1.7.0 — 2026-07-12
 
 ### Added