Add Internal provider for extension-to-extension SMS

[KitaroAI]

New provider that enables internal SMS routing within FreePBX (no external carrier).

• Supports extension-to-extension SMS loopback
• No MMS support
• No external dependencies
• Uses Smsconnector API (getMessage + emitSmsInboundUserEvt)
• Returns 405 for callPublic as it's internal-only

[billsimon]

Tell me more about the use case for this. FreePBX with the softphones and UCP already has user-to-user chat capabilities. What endpoints do you use - Talk mobile, Phone desktop, UCP, sip clients? If you're using strictly SIP clients like Zoiper I actually think a small bit of custom dialplan would work better, but in a mixed environment I can kind of see the value.

[KitaroAI]

I use groundwire as my softphone and this allows me to text another groundwire user. I also use it in conjunction with a custom alteration that checks the db if the DID I am texting is one of mine and if so it will use the ext (local) to send the sms so that it stays within my freepbx setup and I am not charged. Otherwise it will send via telnyx as standard sms. All my users use groundwire as their softphone.

To use the local provider I simply enter the ext number as the DID and choose Internal as the profile.