feat(learn): Explore by what a licence allows, a skeleton while the library loads, and an assistant's agreement per provider (ADR 0005, rule 12; ADR 0021, D66)

- Explore filters by what a studyset's licence lets a learner do: adapt
  it (no NoDerivatives) and use it commercially (no NonCommercial),
  which the instance reads from the release's licence
  (ExploreQuery.adaptable, commercial) and the app the same way
  (LicenseUse). An instance from before ignores both.
- While the studysets are read, the Library shows shimmering skeletons
  of their cards rather than a spinner: halkyon_ui's new Shimmer and
  SkeletonBox, still where the system asks for no animations.
- The scope's "Include private studysets" is offered only while the
  person has a private studyset.
- An agreement to what goes where is per provider (protocol and host):
  agreeing to one assistant agrees to every assistant of that provider,
  those granted later too, and the agreement sheet says so. No
  migration: it is written on every grant of the provider, so taking
  one back keeps it for the others, and read per provider from any of
  them.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_base_server/README.md

@@ -25,7 +25,7 @@ Endpoints, under the nickname `base` in a host's client (`client.modules.base.em
 | `waiting` | with a waiting account's pass (Halkyon Learn's ADR 0021, D31): `look` (waiting, suspended, approved, which takes the pass, or unknown), `deleteAccount` (a new account never approved), `forget` | without a session |
 | `instanceOperator` | `counts` (who waits, operates, has an account: D62), `waiting` (50 from an offset), `approve`, `refuse` (a new account, deleted), `accounts` (by the start of a handle, 50 from an offset), `suspend` (every session ending, the account waiting anew; never an operator), `operators`, `appoint` (by handle, approving one that waits), `takeBack` (never the last operator) | `identified` and `operator`, on the register |
 | `instance` | `basics`: the app it serves, whether codes by mail, password sign-in and SimpleLogin are on, who may sign up (`SIGN_UP`), the source link, the oldest app build, where data and backups are, whether people may add assistants with their own keys | anyone |
-| `assistant` | Halkyon Learn's ADR 0021, step 2: `offered`, the assistants granted to the caller that are set, with what goes where, their effort and whether they agreed, and the caller's budget with what is used of it (none on a member, D43); `agree(assistant)`, to what goes where, its provider as it is now (D40); `ask(question)`, at an effort offered or the operator's default (D63), a stream: the answer's text as the model writes it, then the whole turn with why it stopped and its tokens, once counted (D35, D38); `figures`, the caller's own, month by month | `identified` |
+| `assistant` | Halkyon Learn's ADR 0021, step 2: `offered`, the assistants granted to the caller that are set, with what goes where, their effort and whether they agreed, and the caller's budget with what is used of it (none on a member, D43); `agree(assistant)`, to what goes where, its provider as it is now (D40), and so for every assistant of that provider, those granted later too (D66); `ask(question)`, at an effort offered or the operator's default (D63), a stream: the answer's text as the model writes it, then the whole turn with why it stopped and its tokens, once counted (D35, D38); `figures`, the caller's own, month by month | `identified` |
 | `assistantOperator` | `setUp`: the assistants set, without their keys, with their effort, and how many people have any; `grantees` (by the start of a handle, 50 from an offset) and `granteesOf(accounts)`: each person's assistants, budget and what they used; `grant(accounts, assistants, budget)`: each person the assistants they lack, the agreements of the others kept, and the budget (D58); `change(account, assistants, budget)`: exactly those; `revoke(account)`: every assistant and the budget; `figures(month)`: everyone's of a UTC month, per person and assistant | `identified` and `operator`, on the register |
 | `profile` | `mine`, `save`, `checkHandle` (with every answer about a new handle, at most 30 an hour per person and 60 per network), `checkLinks` (at most 10 an hour), `setAvatar`, `removeAvatar`, `remove` (what it shows goes, the handle stays, private again: Halkyon Learn's ADR 0020, D27): the caller's own public profile | `identified` |
 | `profiles` | `byHandle`: anyone's public profile once they went public, whatever the handle's case | signed in |