refactor: fold machine-remote-data into remote-data.ts, PascalCase load lifecycle (RD-11)

`machine-remote-data.ts` defined a third encoding of an in-flight fetch:
`LoadLifecycle`. It had three call sites, all one identical line, and the type
was never imported by name. Move the mapping into `remote-data.ts` as
`fromLoadLifecycle`, beside its neighbour `fromResource` — a `RemoteData`
constructor, not a sixth encoding.

The lowercase `loading`/`failed`/`loaded` tags on `BriefState`,
`OrgTemplateState` and `StamdataEditorState` existed only because
`LoadLifecycle` required them. Now that the constraint is inline and
PascalCase, the three machines' load-lifecycle tags become `Loading`,
`Failed` and `Loaded` — matching their own PascalCase message tags in the
same file. `stamdata-editor.machine.spec.ts` no longer asserts a PascalCase
message producing a lowercase state.

`BriefStatus` (the letter's draft/submitted/approved/rejected/sent status,
parsed off the wire from `BriefViewDto`) is a separate tag family and is
untouched — its tag count stays 54 before and after this change.

Delete `machine-remote-data.ts` and merge its spec into `remote-data.spec.ts`.
Regenerate `behaviour-spec.mdx` (the `machineRemoteData` section heading
becomes `fromLoadLifecycle`) and confirm `gen:snippets` reports no drift, since
`remote-data.ts` carries a showcase region.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

libs/shared/docs/behaviour-spec.mdx

@@ -819,6 +819,12 @@ classes.
 - is empty-safe: undefined, null, and empty string all yield the empty string
 - returns empty for an unparseable string rather than "Invalid Date"
 
+#### fromLoadLifecycle
+
+- maps Loading → Loading
+- maps Failed → Failure carrying an Error with the reason
+- maps Loaded → Success carrying the whole loaded state
+
 #### httpClientFetch
 
 - sends the pending idempotency key as a header for a write, not a fresh one per attempt
@@ -836,12 +842,6 @@ classes.
 - keeps query + hash on both targets
 - the root maps nl → / and en → /en/
 
-#### machineRemoteData
-
-- maps loading → Loading
-- maps failed → Failure carrying an Error with the reason
-- maps loaded → Success carrying the whole loaded state
-
 #### parseBsn (elfproef)
 
 - accepts a valid BSN (passes the elfproef)