feat(admin): remote Meshtastic node config write (limited fields)

[iceice400]

Summary

• Adds limited remote Meshtastic config writes via ADMIN portnum (names, role, screen timeout, telemetry interval)
• Role changes require typing CONFIRM in DangerousModal; post-write automatic read-back verifies applied state
• Builds on PR feat(admin): remote Meshtastic node config reader via ADMIN portnum #86 read path — includes full ADMIN read + write stack

Part of Master PR Roadmap #16 (FR4). Highest-risk PR in the roadmap — ADMIN write TX.

Writable fields

Field	Notes
long_name / short_name	Owner ADMIN message
role	Device config — requires role_confirm: "CONFIRM"
screen_on_secs	Display config (0–600)
telemetry_interval_secs	Module telemetry config (30–86400)

Blocked: LoRa frequency, PSK/security, factory reset, channel keys.

Risks / notes

• Wrong admin PSK or offline node → write ACK may succeed but verify times out
• Role changes affect mesh routing behavior — extra confirmation required
• Multiple ADMIN packets per apply when several fields change
• Audit: admin.config_write logs target + changed fields only (no secrets)

Test plan

• python -m unittest tests.test_admin_reader tests.test_admin_writer -v (14 tests)
• Shared admin channel on Meshpoint + test node
• Change long/short name — verify owner read-back
• Change role with CONFIRM modal — verify device.role in read-back
• Change telemetry interval — verify module telemetry read-back
• Confirm LoRa/PSK fields rejected server-side

AI-assisted

PR description and implementation assisted by Claude. Follows PR #86 patterns (TxService.send_admin_message, audit, node drawer).