[codex] Add exact MC0 MeshCore DM routing

[n30nex]

What changed

• Makes formal MeshCore MC0 addresses full lowercase 64-hex public keys, with short_id kept as display-only metadata.
• Routes MC0 and on-device MeshCore DMs through a new exact-public-key backend contract instead of resolving a target and then falling back to backend name substring matching.
• Adds key-aware DM readiness (ready, no_key, not_messageable), to_addr/to_name mismatch rejection, and a bounded V0 MC0 NODES response.
• Extends simulator coverage for exact to_addr sends, unambiguous name fallback, duplicate names, missing keys, and mismatched address/name targets.
• Updates the MC0 USB smoke helper to probe IDENTITY and assert addr_format=meshcore-pubkey-hex.
• Fixes scripts/tdeck_smoke.py no-stub esptool argument spellings for the installed esptool version.

Why

MC0 previously accepted to_addr, but the resolved node still collapsed back to a display-name send path in the SX1262 backend. That could misroute DMs when names collide or when one name is a substring of another. MeshCore companion clients need stable public-key identity before the USB/BLE bridge can be treated as a real compatibility surface.

Local validation

• git diff --check
• python -m py_compile scripts\mc_companion_usb_smoke.py scripts\tdeck_smoke.py scripts\fetch_tdeck_artifact.py
• pio run -e native
• .pio\build\native\program.exe --selftest
• .pio\build\native\program.exe --simtest

A local pio run -e tdeck-meshcore sanity compile was attempted before the smoke-script fix but hit the 5-minute tool timeout without useful output. The authoritative firmware binary below came from GitHub Actions.

GitHub Actions artifact

• Workflow run: https://github.com/n30nex/LimitlezzOS/actions/runs/27878289585
• Artifact: tdeck-meshcore-firmware-58755eb715f639ccc2a799d6ea380b3eb667d960
• Manifest: sha=58755eb715f639ccc2a799d6ea380b3eb667d960, env=tdeck-meshcore, meshcore_enabled=1, budget_status=pass
• Size: firmware_bytes=1579984, firmware_slot_pct=30.14, static_ram_bytes=230196

COM8 hardware validation

COM8 only; COM11 and COM29 were present and not targeted.

• Flashed exact artifact with scripts\tdeck_smoke.py --port COM8 --env tdeck-meshcore --no-stub-upload --skip-build --artifact-dir .pio\ci-artifacts\tdeck-mc0-exact-dm-58755eb ...
• Flash target: ESP32-S3 rev v0.2, MAC cc:8d:a2:0d:14:28; bootloader, partitions, boot_app0, and firmware hashes verified by esptool.
• Serial smoke passed: id, sys, companion mc hello, companion mc status, companion mc test.
• Observed MeshCore address: c86a84a412fb64d5adce8114a6b3c0aec881baa0a742a76f9e85c30bc1ad5460; short_id=MC-c86a84a4; MeshCore MC0 protocol selftest: PASS.
• Formal MC0 USB smoke passed: HELLO, IDENTITY, STATUS, NODES, EXIT; IDENTITY reported addr_format=meshcore-pubkey-hex and the same 64-hex pubkey.
• Split-airtime smoke passed on the same artifact, then device state was restored to Meshtastic on, MeshCore on with Balanced airtime.