Document installer-backed node maintenance and recovery

[HDauven]

Summary

• replace the generic maintenance page with an actionable health, resource, log, update, reboot, key-management, and incident-response runbook
• align upgrade and rollback commands with node-installer v0.5.22, including role/network flags, staged downloads, managed-file replacement, target-user behavior, and explicit restart verification
• make fast-sync and recovery guidance role-aware and stop recommending routine unstaking, blind ruskreset, or source-built wallet updates
• update archive installation and canonical GraphQL checks, with an explicit boundary between execution-state snapshots and complete historical archive indexes
• correct consensus-key installation, explorer references, and the transaction-lifecycle description of installer-configured mempool expiry

Closes #21.

Why

The existing maintenance page did not provide the checks or recovery actions requested by the issue. Adjacent pages had also diverged from the current installer:

• stopping Rusk before running the installer defeated its staged-download update flow;
• archive operators could accidentally install the default binary by omitting --feature archive;
• rusk.toml, the systemd unit, helper scripts, and wallet configuration were described as though updates preserved local changes;
• download_state was presented as an archive bootstrap even though it restores execution state rather than pre-snapshot historical indexes; and
• several procedures omitted required root privileges or recommended destructive reset/source-build paths too early.

Validation

• traced node-installer main at e25a191 and released v0.5.22 at ba73650, including install staging, binary verification, file ownership, preserved files, systemd behavior, log rotation, download_state, and ruskreset
• ran bash -n/sh -n over the released installer and helper scripts
• ran the installer-managed ruskquery helper against live mainnet for info, peers, block-height, and installer version; live Rusk reported 1.7.1
• exercised canonical archive GraphQL introspection and checkBlock(... onlyFinalized: true) against the live archive endpoint
• traced Rusk state export and archive storage separately to verify that a state snapshot does not backfill archive indexes
• confirmed Rusk built-in mempool defaults against source and node-installer mainnet/testnet overrides against v0.5.22
• npm run build (Astro build and all internal links)
• Chromium full-page inspection at 1440x1000 and 390x844 for maintenance, upgrade, archive, and troubleshooting pages