Adds an app-aware `fn-verify-app-image` helper that pulls the deployed image
from the configured registry when it is missing locally, gated on
push-on-release being enabled, honoring per-app `registry:login` credentials.
Every in-tree `verify_image` caller migrates to the wrapper and the bare
helper is marked deprecated. `config:set` now forwards the deployed image tag
to `release-and-deploy` so the release path no longer pins recovery on the
unrecoverable `:latest` tag.
Three plugins still leaked the built-in default through `<plugin>-global-<property>` after the broader raw/computed split in #8640. External tooling reading `:report --format json` for drift detection could not distinguish "set to default" from "never set" - after a `:set --global` followed by an unset, the JSON still reported the default value. The `<plugin>-global-<property>` keys now hold the raw stored value (empty when nothing has been set) and `<plugin>-computed-<property>` keys hold the effective value with per-app, global, and built-in default fallback. Every global property now has a computed sibling for shape consistency, including those whose default is empty. Internal callers in `scheduler-k3s` that previously read the default-applied global helpers now consume new `getComputed*` helpers, keeping deploy-time behavior unchanged.
Renames the existing `## Internal properties` umbrella section to `## Properties` across all plugin docs and adds a new `### Settable properties` subsection enumerating every property accepted by each plugin's `:set` command. Each row lists scope, default, the actual `:report` flag shapes that surface the value, and a one-line description. The buildpacks plugin is included even though it uses `:set-property`, with a note in the subsection clarifying the legacy command name. Property lists, scopes, and report flags were verified against plugin source and the live dokku binary.
