docs: rename diagram assets to doc-prefixed scheme, update exports

Asset renames (matching the new Nextcloud source naming convention —
doc name first, then description):
- architecture-trust-depth.svg -> architecture-overview-trust-depth.svg
- firewall-docker-bypass.svg -> firewall-and-network-docker-bypass.svg
- secrets-lifecycle.svg -> secrets-and-pki-lifecycle.svg
- trust-boundaries-blast-radius.svg -> readme-trust-boundaries-blast-radius.svg
Updated all 4 markdown references accordingly.

Also refreshed diagram exports (secret-distribution-flows.svg, and the
4 renamed ones) with today's fixes, and folded in the earlier pending
sso-and-identity.md work: precise live-verified native-OIDC app list
(12 apps, not ~9), the Proxmox no-Proxy-Provider exception, real API
evidence for it, and the automation-bot migration story.

README.md

@@ -41,7 +41,7 @@ Most self-hosted setups have one trust boundary: "you're on the LAN, you're trus
 
 This fleet runs **four trust boundaries, each calibrated to who's actually on the other end** — public internet traffic, human browsers on personal devices, machine-provisioned containers, and non-HTTP infra traffic each get a different control, matched to their real risk, not a blanket policy applied everywhere or nowhere. Enforced by **three independent routing authorities** instead of one central router, specifically so a failure or misconfiguration in any single one only ever takes out its own third of the traffic — never all of it at once. It didn't start this way, either: the public proxy used to be its own VM, and the internal service-to-service model used to be a flat, unauthenticated mesh with no boundary at all. Both got replaced deliberately, trading operational simplicity for a smaller blast radius.
 
-![Trust Boundaries and Blast Radius](assets/trust-boundaries-blast-radius.svg)
+![Trust Boundaries and Blast Radius](assets/readme-trust-boundaries-blast-radius.svg)
 
 The three routing authorities are also split across two separate physical nodes, so a hardware failure is contained the same way a routing failure is — never all three at once.