Export PDF

Keep the selection coherent: one story per PDF. Never mix unrelated assets
(two videos about different things, photos from different events) just to
show more; if the user's material spans several stories, offer one PDF per
story instead.

Args:
    album_id: Album UUID, or asset_ids: explicit asset UUIDs (exactly one of the two).
    output_path: Where to write (default ~/Desktop/<title>.pdf). Existing files are never overwritten.
    title: Cover title (default: album name or "Immich export <date>").
    captions: {asset_id: text} written after looking at the images.
    layout: 'detail' (one asset per page with its data, default), 'grid' (six per page)
        or 'photobook' (one asset per page, image as large as it fits, caption under
        it; a video with several chosen frames unfolds into one full page per frame).
    frames_per_video: Frames per video, evenly spaced (0-120, default 4; 0 = poster only).
    frame_interval: One frame every N seconds instead of frames_per_video (same 120 cap).
    frame_times: {asset_id: [seconds, ...]} exact moments for specific videos, chosen
        after looking at their frames ("the representative frame"). Wins over
        frames_per_video/frame_interval for the listed videos; others keep the spread.
    frame_captions: {asset_id: [text, ...]} one caption per extracted frame, in frame
        order (photobook prints each on its frame's page; other layouts ignore them).
    image_size: 'original' (default): photos go in at the stored file's quality,
        re-encoded to at most 3000px (a format the server cannot decode, like
        some HEIC, falls back to preview with a note); 'preview' (1440px) or
        'thumbnail' for smaller files.
    frame_size: video frame size in the PDF: 'auto' (default, same as 'preview':
        quality is free inside the PDF) or 'thumbnail' for a smaller file.
    language: 'en' (default) or 'es' for the fixed labels on the pages (Index,
        Places, Camera, page numbers); captions stay in whatever language you wrote.
    map: Draw an OpenStreetMap map on the Places page when assets carry GPS
        (default True; tiles come from tile.openstreetmap.org, the only
        third-party call this server makes — pass map=False to skip it).
    cover, index, places: Include each front-matter page (all default True;
        turn them off for a print-ready photobook of bare pages).
    footer: 'full' (plugin name, server and page number, default), 'pages'
        (just the page number) or 'none'.
    header: Repeat the title at the top of every page except the cover
        (default False).
    videos_position: Where the video pages (frame strips or frame pages) go:
        'mixed' with the photos in the general order (default), 'first' or 'last'.
    order: 'auto' (albums read oldest to newest, like the frames inside a video;
        asset_ids keep the order you passed), 'oldest', 'newest' or 'given'.
    confirm: Only asked for when explicit asset_ids mix videos more than 90 days
        apart (different stories). Pass True only when the user themselves asked
        to mix them; exporting a whole album never needs it.
    limit: Max assets (1-500, default 100).
    return_base64: Also return the PDF bytes (skipped above 2 MB; every MB is
        roughly 350k tokens in the conversation).

Returns: JSON {path, pages, bytes, assets_included, assets_skipped:[{id, reason}], warnings:[...]}.