docs: persistent-route guidance for clientless devices + align site-to-site on Networks (#797)

* docs: add persistent-route guidance for clientless devices and align site-to-site on Networks

Step 5 of both site-to-site guides (and the masquerade page) now walk a
first-time admin through persisting a Linux static route end to end:
detect Netplan vs systemd-networkd with `ls /etc/netplan/`, then a clear
Option A / Option B that are framed as alternatives, with the exact
editing mechanics (open in nano, save/exit keys, or a one-paste
systemd-networkd drop-in). Standardize on the `<IFACE>` placeholder with
an `ip -br addr` hint so a literal `eth0` can't silently misconfigure
hosts using predictable interface names.

Update the site-to-site use-case hub to recommend Networks for all
non-exit-node scenarios, rename "Network Routes" to "Routes", and
reconcile the comparison section with the Routes deprecation.

* docs: promote Routes site-to-site recommendation to a deprecation warning

Move the 'use Networks instead' callout above the Architecture section
and make it a Warning, matching the Routes deprecation. Keep the legacy
no-Policy nuance and the Site-to-VPN pointer; rename Network Routes to Routes.

* docs: correct Networks scenario support and mark Routes deprecated

- advanced-configuration: Networks supports all scenarios (VPN-to-Site,
  Site-to-VPN, Site-to-Site), not VPN-to-Site only
- how-routing-peers-work: Routes labeled deprecated, not 'still supported'

* docs: import Note explicitly in site-to-site use-case page

Addresses CodeRabbit: <Note> was used without an explicit import from
@/components/mdx, relying on the global MDX provider.

* docs: repoint site-to-site cross-links to Networks

Site-to-site moved to Networks; update the homelab and cloud use-case
tiles/table and the access-home-devices and cloud-to-on-premise Next
Steps links to /manage/networks/use-cases/site-to-site.

* docs: rename Network Routes to Routes in prose and repoint advanced-config links

Bucket A rename (display text only): rename the 'Network Routes' feature
name to 'Routes' across prose, link labels, table cells, alt text, Tiles
names, and code comments. Headings are deliberately left unchanged to
avoid breaking anchors and inbound links; URL paths (/manage/network-routes)
are unchanged. Generic routing-table mentions and the desktop system-tray
UI label are left as-is.

Also repoint the access-home-devices and cloud-to-on-premise 'Advanced
configuration' Next Steps links from the Routes advanced-config page to
/manage/networks/masquerade.

* Update site-to-site documentation for clarity

Removed outdated information about using Routes for site-to-site connections.

* Update src/pages/manage/networks/use-cases/site-to-site.mdx

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

* Update section title from 'Networks vs Network Routes' to 'Networks vs Routes'

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

src/pages/help/troubleshooting-client.mdx

@@ -576,7 +576,7 @@ Testing the functionality in practice involves:
 
 #### Are Netbird's network routing resources configured?
 
-For Netbird network routing resources configurations you can use either (new) _Networks_ or (old) _Network Routes_.
+For Netbird network routing resources configurations you can use either (new) _Networks_ or (old) _Routes_.
 
 A Network `net-a` should have at minimum: