docs(signal): clarify tool progress support

[helix4u]

What does this PR do?

Clarifies current Signal tool-progress behavior in the user docs. Signal accepts /verbose and can save a per-platform tool_progress mode, but the current gateway suppresses tool-progress bubbles for adapters without message editing support. The previous docs implied Signal could show each progress update as a separate message, which does not match the runtime path.

This docs-only update tells users to keep Signal tool_progress off for now and use the CLI or an editing-capable messaging platform when they need live tool-call visibility.

Related Issue

No issue filed. Follow-up from Discord support thread 1512915763521126460. Related runtime feature work exists separately in #34561.

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 🔒 Security fix
• 📝 Documentation update
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor (no behavior change)
• 🎯 New skill (bundled or hub)

Changes Made

• Updated website/docs/user-guide/configuration.md to say Signal suppresses gateway tool-progress bubbles despite saved non-off modes.
• Added a Signal-specific note in website/docs/user-guide/messaging/signal.md explaining that Signal lacks sent-message editing and currently shows final replies, not live per-tool progress bubbles.

How to Test

1. Read website/docs/user-guide/configuration.md and confirm the display.tool_progress section no longer implies Signal emits separate progress messages.
2. Read website/docs/user-guide/messaging/signal.md and confirm the Signal page explains current tool-progress behavior.
3. N/A: markdown-only docs correction; no docs build run locally.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform: Ubuntu/WSL docs edit review

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A

For New Skills

N/A.

Screenshots / Logs

N/A. Markdown-only docs correction.