feat: add Fluidd sidebar navigation support via Moonraker DB

[bassco]

Summary

Adds Fluidd navigation integration alongside the existing Mainsail navi.json approach. Instead of a file-based sidebar config, Fluidd stores custom navigation links in Moonraker's database. This PR injects a KlipperFleet link via the Moonraker DB API.

Blocked on: fluidd-core/fluidd#1786 (custom navigation links with drag-to-reorder and expandable sidebar)

Changes

• install_scripts/setup_fluidd_navi.py — New script that adds/removes a CustomNavLink entry in Moonraker's DB at uiSettings.navigation.customLinks. Uses a stable UUID v5 id derived from "klipperfleet". Matches entries by id or title for idempotent install/uninstall.
• install_scripts/setup_moonraker.py — Extended with --add-persistent-file and --remove-persistent-file flags to manage persistent_files in any [update_manager <section>] block. Used to register klipperfleet.html in [update_manager fluidd] so Moonraker preserves it across Fluidd updates.
• install.sh — Deploys redirect shim to Fluidd web root, registers it as a persistent file, and injects the DB nav entry.
• uninstall.sh — Removes the DB nav entry, the redirect shim, and the persistent_files registration.

How it works

1. setup_fluidd_navi.py writes to Moonraker's database — the nav link appears in Fluidd's sidebar (users can reorder/hide/delete it via #1786's UI)
2. klipperfleet.html redirect shim is deployed to Fluidd's web root (~/fluidd/)
3. setup_moonraker.py --add-persistent-file fluidd klipperfleet.html ensures Moonraker preserves the shim when Fluidd updates

Reference

• fluidd PR #1802 comment — original analysis of install/uninstall approach

Test plan

• Hold until feat: add custom navigation links with drag-to-reorder and expandable sidebar fluidd-core/fluidd#1786 is merged
• Install on a system running Fluidd — verify sidebar link appears
• Update Fluidd via Moonraker — verify klipperfleet.html survives the update
• Uninstall KlipperFleet — verify sidebar link and shim are removed
• Install on a Mainsail-only system — verify Fluidd steps are skipped gracefully