fix(web): let the player fill the stage

[haribo]

Summary

• The player carried the capture's max-h-full max-w-full — capped downward, never scaled up — and sat small in the stage (let the player fill the stage #232, observed on prod). A video is never compared (ADR 0013): it now fills the stage, object-contain, letterboxed
• Our own pusher recorded at 800×450 (Playwright's default 800×800 fit): recordVideo.size is pinned to the 1280×720 viewport, so the next push carries a full-size source

Test plan

• Full gates: fe-check, fe-test (106), fe-test-e2e with OZALID_PUSH_SELF=1 (64 — the capture spec filmed and pushed at the pinned size)
• Screenshots of the full-stage player, both themes, validated

No existing test modified.

Closes #232