docs(authentik): document the self-serve user-settings flow + password stage

The default-user-settings-flow was missing a PasswordStage, so users could
edit name/email/locale but not their password. Added a PasswordStage
(InbuiltBackend) bound at order 101. Documented the flow's stage table and
the two ORM gotchas (MTI through model, required backends array).

serverAppConfigs-docs/Infrastructure/Authentik.md

@@ -272,6 +272,34 @@ Two secrets live in the host `.env` (git-ignored; placeholders in
   `dankclaw/authentik/quadlet/`, run `./scripts/deploy.sh dankclaw`. Authentik
   migrates the schema on startup.
 
+## Self-serve user-settings flow (password change)
+
+Users change their own account details through the `default-user-settings-flow`
+(`https://auth.franksdank.cloud/if/flow/default-user-settings-flow/`) — the
+target of the homepage footer's "account" link. It is a `stage_configuration`
+designated flow, so it renders every bound `ConfigurableStage` for the logged-in
+user.
+
+Stages, in execution order (the `FlowStageBinding.order` field, not the M2M
+insertion order):
+
+| order | stage | type | what it does |
+|---|---|---|---|
+| 20 | `default-user-settings` | `PromptStage` | intro prompt |
+| 100 | `default-user-settings-write` | `UserWriteStage` | edit name / email / locale |
+| 101 | `default-user-settings-password` | `PasswordStage` | change password (`InbuiltBackend`) |
+
+**The `PasswordStage` was missing until 2026-09-25.** The stock flow only
+carried the prompt + `UserWriteStage`, so users could edit name/email/locale
+but had no way to change their password. The fix: create a `PasswordStage`
+(backend `authentik.core.auth.InbuiltBackend`) and bind it to the flow. Two
+ORM gotchas: `Flow.stages.add()` fails on this through model
+(`Can't bulk create a multi-table inherited model` — `FlowStageBinding` is
+MTI), so create the `FlowStageBinding` row directly with an explicit `order`;
+and `PasswordStage` requires the `backends` array (a bare `name` insert hits a
+`NOT NULL` violation). Verified via the `FlowPlanner` — the plan now lists all
+three stages.
+
 ## Outpost claim cache (`proxysession`) — 403 after a group add
 
 The embedded outpost does not re-evaluate group membership per request. Each