chore(backport): absorb upstream reliability and channel fixes (batch1)

[bitifirefly]

Summary

This PR backports a focused batch of upstream fixes into our codebase with adaptation and tests.

Included changes

• Telegram: outbound remote media URL support with SSRF validation
• Telegram: preserve extension for generic documents
• Telegram: normalize command sender_id for allowlist checks
• Agent: handle non-string memory consolidation payloads
• File tools: resolve relative paths against workspace
• Context: omit empty assistant content entries
• Config: preserve MCP env variable key casing
• Exec safety: avoid false positive on URL format parameters
• CLI cron run: actually execute agent callback
• Cron: service-layer timezone validation + CLI error surface
• Session: scope storage to workspace with legacy migration
• Providers: expose tts/transcription modules via lazy attrs

Validation

• Full test suite passed locally: 376 passed, 5 warnings
• Targeted regressions for each changed subsystem were added and passed.

Notes

• Changes were landed as small commits to keep review and rollback simple.