calendar: add contacts system to prevent recipient address hallucination

Agent hallucinated "xiaojuzi@meta.com" instead of looking up the correct
address from USER.md. Prompting rules can't reliably prevent this, so
recipient validation is now enforced at the tool level.

- Add contact list/add/delete subcommands (vCard .vcf files synced via CardDAV)
- send --to now resolves through contacts: accepts names, name:type, or
  known emails; rejects unknown addresses with available contacts shown
- Multi-email contacts supported with type qualifier (e.g. "小橘子:work")
- Adding contacts and sending are separate operations (no chaining)

skills/calendar/SKILL.md

@@ -20,7 +20,16 @@ See `TESTING.md` for dry-run and live test steps, verification checklists, and t
 - `khal` for reading calendar (optional but recommended)
 - Runs via `uv run` (dependencies managed in `pyproject.toml`)
 
-## Important: Email Sending Rules
+## Important: Recipient Validation
+
+The `send` command **only accepts recipients that exist in the contacts list**. This prevents hallucinated email addresses.
+
+- `--to "小橘子:work"` — resolves contact name + email type
+- `--to "小橘子"` — resolves by name (errors if contact has multiple emails)
+- `--to "user@example.com"` — accepted only if the email exists in contacts
+- Unknown addresses are **rejected** with the available contacts list shown
+
+**Adding contacts and sending invites are separate operations.** Do not add a contact and send to it in the same request — contact additions should be a deliberate, user-initiated action.
 
 Calendar invites are outbound emails. Follow the workspace email rules:
 - **youlu@luyanxin.com -> mail@luyx.org**: send directly, no confirmation needed
@@ -43,6 +52,11 @@ $SKILL_DIR/scripts/calendar.sh reply [options]
 $SKILL_DIR/scripts/calendar.sh event list [options]
 $SKILL_DIR/scripts/calendar.sh event delete [options]
 
+# Manage contacts (used for recipient validation)
+$SKILL_DIR/scripts/calendar.sh contact list
+$SKILL_DIR/scripts/calendar.sh contact add [options]
+$SKILL_DIR/scripts/calendar.sh contact delete [options]
+
 # Manage todos
 $SKILL_DIR/scripts/calendar.sh todo add [options]
 $SKILL_DIR/scripts/calendar.sh todo list [options]
@@ -57,8 +71,9 @@ $SKILL_DIR/scripts/calendar.sh todo check
 ## Sending Invites
 
 ```bash
+# --to accepts contact names (resolved via contacts list)
 $SKILL_DIR/scripts/calendar.sh send \
-  --to "friend@example.com" \
+  --to "小橘子:work" \
   --subject "Lunch on Friday" \
   --summary "Lunch at Tartine" \
   --start "2026-03-20T12:00:00" \
@@ -71,7 +86,7 @@ $SKILL_DIR/scripts/calendar.sh send \
 
 | Flag            | Required | Description                                    |
 |-----------------|----------|------------------------------------------------|
-| `--to`          | Yes      | Recipient(s), comma-separated                  |
+| `--to`          | Yes      | Recipient(s) — contact name, name:type, or known email |
 | `--subject`     | Yes      | Email subject line                             |
 | `--summary`     | Yes      | Event title (shown on calendar)                |
 | `--start`       | Yes      | Start time, ISO 8601 (`2026-03-20T14:00:00`)   |
@@ -182,6 +197,42 @@ $SKILL_DIR/scripts/calendar.sh event delete --match "Allergy Shot" --all
 
 ---
 
+## Managing Contacts
+
+Contacts are stored as vCard (.vcf) files in `~/.openclaw/workspace/contacts/default/` and synced to Migadu CardDAV via vdirsyncer. The `send` command validates recipients against this contact list.
+
+```bash
+# List all contacts
+$SKILL_DIR/scripts/calendar.sh contact list
+
+# Add a contact (single email)
+$SKILL_DIR/scripts/calendar.sh contact add --name "小鹿" --email "mail@luyx.org"
+
+# Add with email type and nickname
+$SKILL_DIR/scripts/calendar.sh contact add --name "小橘子" --email "Erica.Jiang@anderson.ucla.edu" --type work --nickname "小橘子"
+
+# Add a second email to an existing contact
+$SKILL_DIR/scripts/calendar.sh contact add --name "小橘子" --email "xueweijiang0313@gmail.com" --type home
+
+# Delete a contact
+$SKILL_DIR/scripts/calendar.sh contact delete --name "小橘子"
+```
+
+### Sending to Contacts
+
+```bash
+# By name (works when contact has a single email)
+$SKILL_DIR/scripts/calendar.sh send --to "小鹿" ...
+
+# By name + type (required when contact has multiple emails)
+$SKILL_DIR/scripts/calendar.sh send --to "小橘子:work" ...
+
+# By raw email (must exist in contacts)
+$SKILL_DIR/scripts/calendar.sh send --to "Erica.Jiang@anderson.ucla.edu" ...
+```
+
+---
+
 ## Replying to Invites
 
 ```bash