feat(admin): remote Meshtastic node config reader via ADMIN portnum

[iceice400]

Summary

• Adds read-only remote Meshtastic config fetch via ADMIN portnum from the node detail drawer
• One encrypted ADMIN request per click (get_config_request or get_owner_request); live response correlated from RX pipeline
• Requires meshtastic.admin_key_b64 (shared admin channel PSK) and transmit.enabled

Part of Master PR Roadmap #15 (FR4 Remote Node Administration). PR 16 (write path) follows after merge + soak.

Risks / notes

• TX path — one ADMIN packet per request; duty-cycle limits apply
• Target node must share the admin channel PSK; wrong key → timeout (30s)
• Read-only in this PR — no set_config / role writes
• PSK fields redacted in API responses and audit log (admin.config_request)

Test plan

• python -m unittest tests.test_admin_reader -v (8 tests, pass)
• Set meshtastic.admin_key_b64 on Meshpoint + test node (shared admin channel)
• Request device config 1-hop — verify role/names in drawer
• Request owner section — verify long/short name
• Verify 30s timeout + retry UI when node offline
• Verify 429 debounce on rapid clicks
• Verify audit log has no PSK material

AI-assisted

PR description and implementation assisted by Claude. Patterns follow existing TX (TxService), audit (timed_action), and node drawer section layout.