feat(studio): embedded in promptwise, Studio looks like its own Timeline and takes its chat's files - #8

What

Studio embedded in promptwise's Timeline tab looks and behaves like promptwise's own Timeline. Four commits:

1. The tab fit, back (reapplies #6, reverted in #7)

• Embedded, Studio draws no header. The tab's toolbar sends Inspector and Export as promptwise:command, and Studio reports their state as promptwise:state.
• Below a 1000px dock the layout is the preview over the timeline, with one side group shown when Inspector or a selection asks for it.
• A film opens a second in, the stage is lighter, and the agent leads the empty Design panel.

2. The timeline looks like promptwise's

• The toolbar starts with history, the tool, split and zoom. Snapping, ripple, meters, keyframes, beats and the thumbnail and selection zooms open with More.
• Clips are flat blocks with no title band or shadow. A picture's name is a small chip, and a text layer shows its words in the interface's type on the tertiary surface. Effect badges show on the clip in hand.
• A panel alone in its group has no tab to name it.
• Audio clips keep Studio's fill, which their waveform is drawn for.

3. Dividers and the play button

• The dock's dividers no longer light up in the accent colour. Under the pointer or while dragged they show promptwise's sidebar grip, the white pill with three lines.
• The play and pause glyph had a white fill and vanished on the light surface. It is now promptwise's filled play and pause (Remix) in the button's ink.

4. Files dragged out of promptwise's chat land on the timeline

• promptwise's chat drags its images and videos as a JSON list of URLs under application/x-bebra-asset. The timeline takes that drop: each file becomes a clip that plays from its own address, as a converted promptwise timeline's clips do, one after the other from the drop point.
• A remote file's kind comes from its path, its length from its metadata, and a video lands audible, since the project's probe can't reach it. Anything that isn't an http(s) URL is ignored.

Why

In the tab, Studio sat under promptwise's toolbar with a header of its own, three columns that didn't fit, black clip blocks, an accent-coloured divider and a play button nobody could see. And the project's media could only get onto the timeline through Studio's own Assets panel.

Related work

• BebraAI/bebraai#866 adds Export, "Add from the project" and "Ask the agent" to the tab's toolbar. With this PR's header gone, that toolbar still needs an Inspector button that sends promptwise:command; it is not in [CKS-test] perm probe heygen-com/hyperframes#866.
• Nothing ships until a new promptwise-v* release is cut and the sandbox image moves to it.
• feat(studio): fit and polish promptwise's Timeline tab #6 was reverted in revert: fit and polish promptwise's Timeline tab (#6) #7 "as asked". The reason isn't written down in either PR, so whoever asked should look at this before it merges.

Checked

• bun run lint, Studio's tsc --noEmit and its whole test suite (8214 passed).
• New tests: the embedded toolbar and its More button, a promptwise drop placed in order with a non-http URL ignored, and a remote file's kind and src.
• By hand in the dev Studio inside a frame: the layout at the tab's width, the clips, the grip on both dividers, the play button, More, and a drop with promptwise's payload, which wrote a <video> with the file's full address and its probed length.

Not checked

• A real mouse drag from promptwise's chat into the frame across origins. Browser automation can't start a native drag, so the drop was dispatched as an event inside the frame.
• A dropped remote clip shows "waveform unavailable" on its audio lane.
• Nothing ran in promptwise's sandbox or behind its Studio proxy.

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