v2.12.3 - Auto-Welcome Bug Fixes

This patch release fixes critical bugs in the Auto-Welcome feature introduced in v2.12.0.

What's Changed

Fixed Auto-Welcome emoji missing in Auto-Announce - The hand emoji (👋) now correctly appears in the {FEATURES} token when Auto-Welcome is enabled
Fixed Auto-Welcome spam bug - Nodes are now only welcomed once (removed buggy 24-hour cooldown that caused re-welcoming)
Added thundering herd prevention - Existing nodes are marked as welcomed on container startup to prevent mass welcome messages

Added Auto-Welcome feature check in all three locations where {FEATURES} token is processed
Removed flawed 24-hour cooldown logic that would re-welcome nodes
Added startup logic to mark all existing nodes as welcomed when Auto-Welcome is enabled
New database method markAllNodesAsWelcomed() to prevent thundering herd on restart
Updated tests to match once-only welcome behavior

src/server/meshtasticManager.ts - Added emoji check, fixed spam bug
src/server/server.ts - Added startup thundering herd prevention
src/services/database.ts - Added markAllNodesAsWelcomed() method
src/server/announceTokens.test.ts - Updated tests for Auto-Welcome
src/server/meshtasticManager.autowelcome.test.ts - Fixed tests for once-only behavior
package.json, helm/meshmonitor/Chart.yaml - Version bump to 2.12.3
package-lock.json - Regenerated

No breaking changes. This is a drop-in replacement for v2.12.2.

If you're using Auto-Welcome:

```bash
docker pull ghcr.io/yeraze/meshmonitor:2.12.3
```

```bash
helm repo update
helm upgrade meshmonitor meshmonitor/meshmonitor --version 2.12.3
```

Full Changelog: v2.12.2...v2.12.3