feat: one generic image, with installed modules in installation-owned storage (ADR 0048)

The production image now contains zero feature modules and is the same for every
installation. Installed modules live in module storage that one Core resolver
selects from EKKLESIA_MODULES_DIR: the checkout's modules/ when unset, an
absolute path that must exist when set (/var/lib/ekklesia/modules in the image).
A relative, blank, missing, or unreadable configured directory fails closed with
a sanitized error that never contains the value.

- Host configuration reads EKKLESIA_MODULES_DIR. The API, migration plan, apply
  and validate, module validation, module enablement, and Doctor all resolve it
  the same way; the test-only API override still takes precedence.
- Doctor receives Core's migrations directory explicitly instead of deriving it
  from the modules directory's parent.
- The migration runner retains and reports the applied history of a module that
  is not installed, and plans and applies Core's and present modules' migrations
  around it. Core's history and every installed module's history stay strict: a
  missing or changed applied migration, or a downgrade, still fails. No down
  migrations, no data deletion.
- deploy/Dockerfile copies no module and installs nothing for the module
  template; .dockerignore excludes modules/ and the build refuses a context that
  contains it; the runtime has an empty root-owned /var/lib/ekklesia/modules and
  sets EKKLESIA_MODULES_DIR.
- deploy/compose.yaml bind-mounts EKKLESIA_MODULES_HOST_DIR read-only into api
  and migrate, with create_host_path disabled.
- scripts/check-image.sh proves the image holds no modules and that a populated
  modules/ directory leaves its runtime file system identical; CI runs it.
- The split deploy smoke now uses the same generic image: it boots with no
  modules, installs a self-contained test module packaged from the template
  (test-only), migrates and restarts, removes it (Core runs, planning reports the
  retained history, data survives), and restores it with its data.

Docs: deploy README (module storage, install/update/remove/restore, the runtime
modules target), .env.example, API configuration, module development guide,
testing, workflow, security, and the architecture overview.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/development/authorization.md

@@ -173,8 +173,9 @@ integration layer depends on authorization).
 exact same installed-module inventory every time it starts, in a fixed order, before anything
 else:
 
-1. Resolve module-discovery configuration (the repository's `modules/` directory, and the
-   platform/Module SDK versions from their own `package.json` files).
+1. Resolve module-discovery configuration: the installed-modules directory, chosen by Core's one
+   resolver from `EKKLESIA_MODULES_DIR` (the repository's own `modules/` when it is unset, ADR
+   0048), and the platform/Module SDK versions from the platform's own `package.json` files.
 2. Discover installed modules exactly once (`discoverModules`).
 3. Compose the platform permission registry from that exact discovered list
    (`composePlatformPermissionRegistry`).
@@ -199,7 +200,8 @@ never falls back to `CORE_PERMISSION_REGISTRY` or any Core-only registry. The re
 resolved from this compiled/source file's own location (two directories up from
 `apps/api/dist/*.js` or `apps/api/src/*.ts`, which sit at identical depth), never `process.cwd()`
 — a package-scoped test run has `apps/api` as its working directory, which would otherwise point
-discovery at the wrong `modules/` directory.
+discovery at the wrong `modules/` directory. A configured `EKKLESIA_MODULES_DIR` that is not an
+absolute path to an existing directory fails at step 1, before anything else exists.
 
 The resulting registry is a **static, immutable snapshot** taken once at startup. There is no hot
 installation, removal, or dynamic mutation of installed modules or their permissions while the