feat(tools): add phone_call tool for outbound AI voice calls

[mormio]

## What does this PR do?

Add `phone_call` and `phone_call_result` tools for making outbound
phone calls via AI voice agents. Enables the agent to schedule
appointments, make reservations, and deliver messages by phone on
the user's behalf.

Two providers supported (user chooses during first-time setup):

- **Bland.ai** (default): all-in-one, one API key, built-in voices
- **Vapi**: flexible platform — plug in any voice provider
  (ElevenLabs, Deepgram, PlayHT) and telephony (Twilio, Vonage,
  Telnyx). Better voice quality, more setup.

Provider selected via config.yaml or env vars. Tools only appear
when at least one provider is configured (check_fn gates them).

## Related Issue

No existing issue — this is a new capability.

## Type of Change

- [x] ✨ New feature (non-breaking change that adds functionality)

## Changes Made

- `tools/phone_tool.py`: new tool module — `phone_call` (initiate
  outbound call) and `phone_call_result` (poll for transcript/status)
- `toolsets.py`: add "phone" toolset definition + add both tools
  to `_HERMES_CORE_TOOLS`
- `model_tools.py`: add `tools.phone_tool` to `_discover_tools()` list

## How to Test

**Bland.ai (quick):**
1. Sign up at https://app.bland.ai (free, ~$2 trial credit)
2. Set `BLAND_API_KEY` env var
3. Run: `hermes -q "Call +15551234567 and ask what time they close"`
4. Agent should confirm before dialing, make the call, then report transcript

**Vapi (better voice quality):**
1. Sign up at https://dashboard.vapi.ai + https://twilio.com
2. Buy a Twilio number, import into Vapi
3. Set `VAPI_API_KEY` and `VAPI_PHONE_NUMBER_ID`
4. Set `phone.provider: vapi` in config.yaml
5. Same test as above

**Without any provider configured:**
- Tools should not appear in the agent's tool list (check_fn returns False)

## Checklist

### Code
- [x] I've read the Contributing Guide
- [x] My commit messages follow Conventional Commits
- [x] I searched for existing PRs to make sure this isn't a duplicate
- [x] My PR contains only changes related to this feature
- [x] I've run `pytest tests/ -q` and all tests pass
      (same 8 pre-existing collection errors on main and this branch)
- [ ] I've added tests for my changes — not yet, would appreciate
      guidance on mocking external API calls in the test suite
- [x] I've tested on my platform: Ubuntu (Linux)

### Documentation & Housekeeping
- [ ] I've updated relevant documentation — N/A (tool is
      self-documenting via schema descriptions)
- [ ] I've updated cli-config.yaml.example — should add phone
      section, happy to do in a follow-up
- [ ] I've updated CONTRIBUTING.md or AGENTS.md — N/A
- [x] I've considered cross-platform impact — uses only `requests`
      library, no OS-specific code
- [x] I've updated tool descriptions/schemas

## Screenshots / Logs

Tested with real calls via both providers:

Bland.ai call

phone_call(<phone_number_hidden>, "Deliver a message from Morgane")
→ call_id: b1c18c55-...
→ Transcript: AI delivered message, user responded

Vapi + ElevenLabs + Twilio call

phone_call(<phone_number_hidden>, "Test voice quality")
→ call_id: 019cd87a-...
→ Transcript: User confirmed voice quality improvement