feat: add Matrix channel support

[horsley]

📝 Description

This PR adds first-class Matrix channel support to PicoClaw, including gateway integration, config/defaults, tests, launcher UI updates, and both Chinese/English documentation.

It also fixes a migration bug where OpenClaw channels.matrix.enabled could be ignored and incorrectly forced to true during migration.

🗣️ Type of Change

• 🐞 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 📖 Documentation update
• ⚡ Code refactoring (no functional changes, no api changes)

🤖 AI Code Generation

• 🤖 Fully AI-generated (100% AI, 0% Human)
• 🛠️ Mostly AI-generated (AI draft, Human verified/modified)
• 👨‍💻 Mostly Human-written (Human lead, AI assisted or none)

🔗 Related Issue

• Related to previous Matrix work: feat(channels/matrix): add Matrix channel integration #356

📚 Technical Context (Skip for Docs)

• Reference URL:
  • https://spec.matrix.org/
  • feat(channels/matrix): add Matrix channel integration #356
• Reasoning:
  • Matrix is a common self-hosted/federated channel target for PicoClaw users.
  • Keep channel behavior consistent with existing channel abstractions (group trigger, placeholder, media handling, allow list).
  • Migration should preserve source config semantics (enabled=false must remain disabled).

🧪 Test Environment

• Hardware: PC (x86_64)
• OS: Ubuntu (container/dev environment)
• Model/Provider: N/A for this change (channel + config + migration + docs)
• Channels: Matrix

📸 Evidence (Optional)

Click to view Logs/Screenshots

go test ./... passed locally.

☑️ Checklist

• My code/docs follow the style of this project.
• I have performed a self-review of my own changes.
• I have updated the documentation accordingly.

[CLAassistant]

All committers have signed the CLA.

[horsley]

Follow-up comparison with #356 for reviewer context:

Compared with #356, this PR additionally aligns Matrix support with the current PicoClaw architecture and contributor workflow:

1. Current channel structure + tests
   • Uses pkg/channels/matrix/ (init.go + matrix.go + matrix_test.go) instead of a single legacy file.
2. Broader product integration
   • Adds launcher UI support (TUI + Web), gateway helper wiring, config defaults/tests, and README/README.zh updates.
3. OpenClaw migration support (with bug fix)
   • Includes Matrix migration mapping and preserves channels.matrix.enabled=false correctly during migration.
4. Media path aligned to unified pipeline
   • Covers inbound/outbound media in channel behavior, with MediaStore-based handling/fallback and encrypted attachment decryption support.
5. Bilingual channel docs
   • Adds both docs/channels/matrix/README.md and docs/channels/matrix/README.zh.md.
6. Cleaner scope for mergeability
   • Avoids coupling Matrix channel introduction with unrelated voice/TTS/transcriber/message-tool changes.

So this PR is intended as a more merge-ready Matrix integration pass for the current codebase.

[horsley]

Follow-up fix pushed in commit 64b99b3:

• Matrix group mention detection now also recognizes matrix.to anchor mentions from formatted_body, including URL-encoded forms such as %40user%3Aserver.
• Added a dedicated debug log when a group message is filtered by trigger rules: Ignoring group message by trigger rules.

This should help diagnose the "@mention in group has no response" behavior more clearly.

[Orgmar]

@horsley Matrix channel support with gateway integration, config defaults, tests, launcher UI, and bilingual docs all in one PR, that's a thorough contribution. Also good catch fixing the migration bug where channels.matrix.enabled could get forced to true incorrectly.

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