feat(lagoon): per-query collation for OrderBy, drop the database locale check

- lagoon.OrderBy takes variadic lagoon.OrderOption values; lagoon.Collate(name)
  emits a validated, double-quoted COLLATE clause (e.g. "pl-x-icu")
- remove the exported CheckLocale and the ICU pl-PL check from Open and Use
- framework test containers and per-test databases are plain PostgreSQL
- lagoon README, root README and docs pages drop the locale requirement;
  queries-and-pagination gains a "Sorting with a collation" section
  backed by ExampleCollate

README.md

@@ -12,7 +12,7 @@ SummerCMS is a content management framework for Go, inspired by WinterCMS. An ap
 ## Requirements
 
 - Go 1.27.
-- PostgreSQL 16 for any application that uses the data layer ([lagoon](modules/lagoon/README.md)). lagoon currently requires the database's default locale to be ICU `pl-PL`; see [Known issues](#known-issues).
+- PostgreSQL 16 for any application that uses the data layer ([lagoon](modules/lagoon/README.md)).
 - Node.js 22.6 or newer, only when working on the admin SPA in `admin/`.
 - Docker, only for the integration tests that start PostgreSQL or Mailpit containers through testcontainers-go.
 
@@ -32,10 +32,10 @@ summer build          # generates plugins.gen.go and main.go, writes bin/hello
 
 The `migrate`, `migrate:status`, `migrate:rollback`, `serve` and admin commands open PostgreSQL, so they need more configuration. Configuration comes from YAML files in `config/`, and any key can be overridden with a `SUMMER_`-prefixed environment variable in which a double underscore separates path segments (see [compass](modules/compass/README.md)):
 
-1. Create a PostgreSQL 16 database with the locale lagoon checks for:
+1. Create a PostgreSQL 16 database:
 
    ```sql
-   CREATE DATABASE hello TEMPLATE template0 ENCODING 'UTF8' LOCALE_PROVIDER icu ICU_LOCALE 'pl-PL';
+   CREATE DATABASE hello;
    ```
 
 2. Add the request body limits that `serve` and `route:list` require. The example does not ship them yet, and surf needs numeric values, which the string-valued environment overlay cannot supply. Create `config/http.yaml` in `examples/hello`:
@@ -64,7 +64,6 @@ The `migrate`, `migrate:status`, `migrate:rollback`, `serve` and admin commands
 ### Known issues
 
 - `examples/hello` has no `http.body_limits` configuration, so `serve` and `route:list` fail with `surf: config http.body_limits.default_bytes is required` until you add it as in step 2. The same gap makes the example's `TestTypedItemRoute` fail.
-- lagoon refuses any database whose default locale is not ICU `pl-PL`.
 - The committed `examples/hello/main.go` is older than what `summer build` generates now, so building the example (or running its tests, which build it) leaves that file modified. Restore it with `git checkout -- examples/hello/main.go` if you do not intend to commit it.
 
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