Fix chat history truncation and remaining node_num==0 falsy checks

[hardcoreerik]

Summary

• MonitorStore.read_messages() sorted ORDER BY observed_at ASC LIMIT ? — once a user's message table exceeds the 5000-row default loaded at startup, this returned the oldest N messages and silently dropped every message newer than that, instead of showing recent chat history. Now selects the newest N (using rowid as a deterministic tiebreaker for same-timestamp rows), then re-sorts that selection chronologically for display.
• Two remaining if value truthiness checks on node_num/to fields that mishandle a legitimate node_num == 0 or to == 0 (most instances of this bug class were already fixed in earlier PRs — these two were missed):
  • _device_summary(): NodeDB lookup and node-id formatting both skipped for local_num == 0.
  • _on_text_received(): to_num = packet.get("to") or packet.get("toNum") would fall through to toNum even when a genuine to == 0 was present.

Risk assessment

Low risk, isolated correctness fixes. No schema changes, no behavior change for the common case (table under the limit). read_messages()'s new query is a subquery + re-sort, tested against >limit, under-limit, DM/channel-mixed, and same-timestamp-tiebreak cases.

Test plan

• pytest -q — 361 passed (25 new: test_monitor_store_message_history.py, test_zero_value_handling.py)
• ruff check src tests scripts — clean
• mypy src/meshchat — clean
• Regression tests cover: >5000 messages returns newest N in chronological order; DM and channel messages both survive the newest-N cut; under-limit case unaffected; node_num == 0 NodeDB lookup/id formatting; to == 0 inbound packet resolves as a direct message instead of falling through to toNum.

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Review details

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Configuration used: defaults

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Run ID: 44489871-929e-48f3-ae1c-77fa9a35270d

📥 Commits

Reviewing files that changed from the base of the PR and between be8d113 and 6f7c4d6.

📒 Files selected for processing (5)

• src/meshchat/controllers/meshtastic_controller.py
• src/meshchat/database/schema.py
• src/meshchat/services/monitor_store.py
• tests/test_monitor_store_message_history.py
• tests/test_zero_value_handling.py

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