feat(moa): add Album (Moa) REST service

[enkunkun]

Description

Adds MoaService, wired up as client.base.moa, exposing the LINE Album
(Moa) subsystem. This subsystem was previously unreachable through LINEJS —
users had to hand-craft HTTP requests against the LEGY proxy to list albums
or download original photos.

Unlike Talk / Square, Moa is plain HTTP JSON on top of the LEGY proxy,
not Thrift, so this service uses client.fetch directly with an
X-Line-ChannelToken issued via
channel.approveChannelAndIssueChannelToken({channelId: "1375220249"}).

API

// List all albums (paginate via cursor)
const resp = await client.base.moa.getAlbums({ cursor: "" });
for (const album of resp.result?.albums ?? []) {
  console.log(album.title, album.photoCount);
}

// List photos in an album
const photos = await client.base.moa.getPhotos({
  chatId, albumId, cursor: "", pageSize: 100,
});

// Download original bytes (image or video)
const bytes = await client.base.moa.downloadPhoto({
  chatId, albumId, oid: photo.obsResourceId!.oid!,
  prefix: photo.obsResourceId?.sid === "v" ? "album/v" : "album/a",
});

buildMoaUrl is exported as a pure helper for anyone wanting to hand-craft
additional Moa endpoints (the AB service in CHRLINE covers ~30 more).

Header override caveat

The Moa REST endpoints require accept: application/json. The default
client.base.request.getHeader("GET") returns
accept: application/x-thrift, which causes LEGY to reject Moa requests
with {"code":102001,"message":"一時的なエラーが発生しました。"} at HTTP 200.
MoaService handles this override internally.

What changed

• packages/linejs/base/service/moa/mod.ts (new) — MoaService +
  buildMoaUrl helper + response type interfaces.
• packages/linejs/base/service/moa/mod.test.ts (new) — 5 tests
  covering buildMoaUrl edge cases (custom endpoint, encoding, undefined
  skipping).
• packages/linejs/base/service/mod.ts — re-export MoaService.
• packages/linejs/base/core/mod.ts — register
  client.moa = new MoaService(this) alongside other services.
• docs/docs/moa.md (new) + sidebar entry — usage examples and the
  Accept-header caveat.

Verified end-to-end

Against a live LINE account:

• getAlbums({}) returned 100 albums (first page)
• getPhotos({chatId, albumId}) returned photo metadata with
  obsResourceId, shotTime, etc.
• downloadPhoto({...oid}) returned the original JPEG (245 KB) matching
  the LINE app's saved copy byte-for-byte

Checklist

• MoaService verified against live LINE (list + list-photos + download)
• Unit tests for buildMoaUrl (5 cases)
• Documentation page + sidebar link
• Follows existing service registration pattern in BaseClient