Add dial-in/out and DTMF event handlers to all phone bots

[vr000m]

Summary

• Add full dial-in event handlers (on_dialin_ready, on_dialin_connected, on_dialin_stopped, on_dialin_warning, on_dialin_error) to all dial-in and transfer bots
• Add missing dial-out event handlers (on_dialout_connected, on_dialout_stopped, on_dialout_warning) to PSTN dial-out and cold-transfer bots
• Add on_dialout_warning to warm-transfer bot
• Add on_dtmf_event handler to all PSTN bots (Twilio bots already had it)
• Fix on_dialin_ready signature: use sip_endpoint param to match pipecat API
• Fix "Handling call from" to "Handling call to" for To field logging
• Fix NameError in cold-transfer bot where request was undefined
• Add caller/callee logging to cold-transfer bot
• Improve log prefixes in warm-transfer (e.g., "Supervisor dial-out connected")
• Remove sip_caller_phone workaround in dial-out bots (fixed in pipecat 0.0.107 via enable_dialout should not depend on sip_caller_phone being set pipecat#4087)

Test plan

• Dial-in bots: verify all dial-in events are logged during a call
• Dial-out bots: verify all dial-out events are logged during a call
• Transfer bots: verify both dial-in and dial-out events are logged
• DTMF: press keypad during a call, verify DTMF events are logged
• Cold-transfer bot: verify no NameError on startup
• Dial-out bots: verify rooms are created with enable_dialout without sip_caller_phone workaround (requires pipecat >= 0.0.107)