docs: name the specific daemon instead of the vague 'backend'

Per mara's ruling on hyperhive#4041 (Microsoft.Avoid): 'backend' never says
which system it means. Fixed all 21 fixable hits to name the actual daemon
(mostly hive-c0re; one hive-agent instance and one hive-matrix-daemon one,
both confirmed against surrounding context, not guessed). Also tightened
Weston's own 'VNC backend'/'RDP backend' plugin references to their literal
upstream names (vnc-backend/rdp-backend) rather than dropping the accurate
term entirely, and reworded one unrelated Microsoft.Avoid hit ('and so on').

Left alone (flagged on the issue, not guessed): docs/turn-loop/config.md's
3 remaining hits match the actual nix option name (backendEnvironmentFile)
and describe a genuinely pluggable concept (which LLM API provider), not
one specific internal system.

docs/networking/gateway.md

@@ -49,7 +49,7 @@ For matrix / per-agent static assets, `<final>` is `=404` (a missing asset is ju
 
 ### Dashboard: path-based routing (not Accept-header)
 
-Every hive-c0re backend route lives under `/api/` plus the single `/webhook/knowledge` endpoint, so the dashboard vhost routes by **path**, not Accept header — deterministic, unlike a content-type split where the same URL could resolve differently depending on the caller's `Accept` header:
+Every hive-c0re route lives under `/api/` plus the single `/webhook/knowledge` endpoint, so the dashboard vhost routes by **path**, not Accept header — deterministic, unlike a content-type split where the same URL could resolve differently depending on the caller's `Accept` header:
 
 - `location /api/` → hive-c0re (`7000`): all dashboard data, actions/mutations, and the two SSE streams (`/api/dashboard/stream`, `/api/build-logs/id/{id}/stream`). Carries `proxy_buffering off` + a 1d read timeout for the streams.
 - `location /webhook/` → hive-c0re: the knowledge webhook.