feat: add callout shortcode (note/tip/info/warning/danger/success)

- Single shortcode with type param, CSS-only variants
- Left border + fading bottom border (::after gradient)
- Colors mapped to existing theme tokens (--accent, --accent2, --type-link, --type-life)
- --callout-danger: #ef4444 hardcoded exception (approved)
- role=alert for danger, role=note for all others (WCAG AA)
- aria-hidden on Feather icons, title overridable via param
- EN/IT i18n keys

Also fixes html.theme-light CSS vars to match THEMING-STANDARD.md:
- --bg, --bg2, --surface, --border, --text, --text-dim, --muted
- --accent (#7c3aed), --accent2 (#008f5a)

2 files changed, 16 insertions, 0 deletions

diff --git a/i18n/en.yaml b/i18n/en.yaml
index 0dfb811..c328748 100644
--- a/i18n/en.yaml
+++ b/i18n/en.yaml
@@ -177,3 +177,11 @@ repo_example_2_desc:
   other: "SlackBuild scripts for Example Package 2. A comprehensive package with full documentation and support."
 repo_example_3_desc:
   other: "SlackBuild scripts for Example Package 3. Utility package for system administration and configuration."
+
+# Callout shortcode titles
+callout_note: "Note"
+callout_tip: "Tip"
+callout_info: "Info"
+callout_warning: "Warning"
+callout_danger: "Danger"
+callout_success: "Success"
diff --git a/i18n/it.yaml b/i18n/it.yaml
index 3114c57..ff3a80a 100644
--- a/i18n/it.yaml
+++ b/i18n/it.yaml
@@ -179,3 +179,11 @@ repo_example_2_desc:
   other: "Script SlackBuild per Pacchetto Esempio 2. Un pacchetto completo con documentazione e supporto completi."
 repo_example_3_desc:
   other: "Script SlackBuild per Pacchetto Esempio 3. Pacchetto di utilità per amministrazione di sistema e configurazione."
+
+# Titoli shortcode callout
+callout_note: "Nota"
+callout_tip: "Suggerimento"
+callout_info: "Informazione"
+callout_warning: "Attenzione"
+callout_danger: "Pericolo"
+callout_success: "Successo"