Ability to pin multiple shared screens (and tiles) at once

[Crash--]

Feature Request

Is your feature request related to a problem or unsupported use case? Please describe.
When several participants share their screen at the same time, only one tile can be pinned (in focus) at a time. Pinning a new tile replaces the previous one, so it's impossible to keep multiple shared screens visible side by side.

This is limiting in several common scenarios:

• Comparison / collaboration: following two shared screens at once during a code review, a design comparison, or a multi-document walkthrough.
• Accessibility: keeping a presenter's shared screen and a sign-language interpreter's video in focus simultaneously — a key use case for deaf and hard-of-hearing participants.

Describe the solution you'd like
Allow a participant to pin more than one tile (screen share and/or camera) at the same time:

• The pin/unpin action toggles each tile independently, instead of replacing the current focus.
• Pinned tiles are displayed together in a responsive grid (focus area), while non-pinned tiles move to the carousel.
• Unpinning a tile returns it to the grid without affecting the other pinned tiles.
• A reasonable upper bound should be enforced so the focus grid stays readable (Zoom allows up to 9, Google Meet up to 3 — a small cap such as 3–4 seems sensible to start).

This pin state remains local to each participant (no impact on others), consistent with the current pin behavior.

Describe alternatives you've considered

• Keeping the current single-pin behavior and relying on the gallery/grid view to see other screens — but it doesn't let the user choose which tiles stay in focus, and shared screens get small among camera tiles.
• A global "pin for everyone" (see Pin for everyone #528) — useful, but solves a different problem: it's host-controlled and forces a single shared focus, whereas this request is about each participant choosing several tiles for their own view.

Prior art

• Zoom — "Multi-Pin": pin up to 9 tiles locally; the global equivalent ("Spotlight") is a separate feature.
• Google Meet — pin multiple tiles locally; hosts can also pin up to 3 tiles for everyone, introduced largely for accessibility (presenter + sign-language interpreter).

Relationship to existing issues
This is the local / multi-pin counterpart of #528 ("Pin for everyone"), which covers the global admin-controlled pin. The two are complementary and not duplicates: #528 forces a single focus for all participants, whereas this request lets each participant choose several tiles for their own view.

Discovery, Documentation, Adoption, Migration Strategy

• The existing "Pin" action in the tile context menu keeps the same entry point; only its behavior changes from single-focus to multi-focus.
• The focus layout needs to handle an arbitrary (capped) number of pinned tiles in a responsive grid.
• No migration needed — current single-pin usage is just the n=1 case of the new behavior.

Do you want to work on it through a Pull Request?
Yes, I'd like to work on this. Happy to coordinate on the approach before starting the implementation.

Open questions
Is there already any ongoing reflection or discussion on this topic? Or even early ideas on how it should be implemented?