[PATCH datacenter-manager v3 07/12] docs: add subscription registry chapter

[Thomas Lamprecht <t.lamprecht@proxmox.com>]

Cover the Subscription Registry view and the actions it exposes,
together with the permission model the registry enforces.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
---

Changes v2 -> 3:
* Picks up the renamed Discard Pending button (was Clear Pending in
  v2).
* Action paragraphs for Clear Key, Adopt Key / Adopt All, and Check
  Subscription are added incrementally in their respective per-feature
  commits, not here.

 docs/index.rst                 |  1 +
 docs/subscription-registry.rst | 55 ++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)
 create mode 100644 docs/subscription-registry.rst

diff --git a/docs/index.rst b/docs/index.rst
index 2fc8a5dc..2aaf86ea 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -27,6 +27,7 @@ in the section entitled "GNU Free Documentation License".
    remotes.rst
    automated-installations.rst
    views.rst
+   subscription-registry.rst
    access-control.rst
    sysadmin.rst
    faq.rst
diff --git a/docs/subscription-registry.rst b/docs/subscription-registry.rst
new file mode 100644
index 00000000..f1e6fd5b
--- /dev/null
+++ b/docs/subscription-registry.rst
@@ -0,0 +1,55 @@
+Subscription Registry
+=====================
+
+The subscription registry maintains a central pool of Proxmox VE and Proxmox Backup Server
+subscription keys and lets an administrator assign them to remote nodes from a single place, without
+having to select and configure a key for all remote nodes individually.
+
+Key Pool
+--------
+
+The pool accepts Proxmox VE and Proxmox Backup Server keys; other key prefixes are rejected so that
+a new product type is noticed instead of silently parking unusable entries. Each entry records its
+origin and the optional remote node it has been assigned to.
+
+Keys can be added in bulk from the web interface or with the ``proxmox-datacenter-client
+subscriptions add-keys`` command. The Add dialog takes multiple keys, separated by newlines or
+commas, and validates the whole batch atomically.
+
+Node Subscription Status
+------------------------
+
+The Node Subscription Status panel shows the live subscription state of every node behind a
+configured remote alongside any pending plan from the pool. Nodes that already hold a key the
+registry assigned appear with the live level; nodes with a pending pool assignment show a clock
+icon until the change is pushed to the remote.
+
+From this view an operator can clear a pending assignment or remove the key from the pool entirely,
+which is convenient when a node is known to be wrong without first having to find the matching entry
+on the key list.
+
+Assignment
+----------
+
+A key can be pinned to a single node manually.
+
+The Auto-Assign action proposes a plan that fills unsubscribed nodes from free pool keys. For
+Proxmox VE, the smallest covering key by socket count is chosen, so a 4-socket key is not used on a
+2-socket host while a larger host stays unsubscribed.
+
+The proposed plan can be inspected before it is applied. Apply Pending pushes the queued keys to
+their target nodes; if a push fails the remaining queue is kept intact for retry. Discard Pending
+drops the plan without touching any remote.
+
+Permissions
+-----------
+
+Listing the pool and the node status view follows the regular audit privileges on each affected
+remote. Pool entries pinned to a remote the operator has no audit privilege on are hidden from
+the listing; unbound entries stay visible to anyone with the system-scope audit privilege.
+
+Any mutating action on a pool entry or its remote binding requires the matching resource
+privilege on the target remote in addition to the system-scope MODIFY privilege, so an
+operator with global system access alone cannot drive changes against remotes they have no
+other authority on. Auto-Assign skips remotes the caller cannot modify, so a previewed plan
+never silently commits an assignment on a remote the operator only had audit on.
-- 
2.47.3