Polish huddles UI

[klopez4212]

Summary

• Reworks the active huddle bar into a revealed bottom drawer with rounded app corners, centered controls, and theme-aware surfaces.
• Simplifies huddle actions by removing the pre-join headphones gate and end-for-all control, then moves participants, agents, speaker settings, and mic settings into compact controls/popovers.
• Adds huddle reaction events plus local/remote emoji bursts, and tunes mic feedback with a compact low/mid/high waveform meter.

Checks

• just fmt-check
• cargo check -p buzz-core
• cargo check --manifest-path desktop/src-tauri/Cargo.toml
• cd desktop && pnpm exec biome check <changed desktop files>
• cd desktop && pnpm check:file-sizes
• cd desktop && pnpm typecheck
• cd desktop && pnpm test
• cd desktop && pnpm build
• git diff --check

Note: cd desktop && pnpm check is still blocked by pre-existing unused-variable warnings in desktop/tests/e2e/onboarding.spec.ts, outside this branch.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Restore creator end-huddle action

When the local user is the huddle creator and other humans remain, this now only renders the Leave action, so the creator has no UI path to call end_huddle. The backend leave_huddle only emits the ended event and archives the ephemeral channel when the leaver is the last human; otherwise it just removes the caller, leaving the huddle running for everyone else. This regresses the previous End for all button for creators and can leave meetings active until every participant leaves or the TTL expires.

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