refactor: roll out theme tokens and stabilize watch flows

[Priveetee]

Summary

• roll out persisted dark/light theming with a navbar toggle and semantic color tokens across components, routes, and settings while keeping playback visual behavior stable.
• fix watch regressions by restoring comments below the player on mobile, replacing infinite comment loading with explicit Load more, and scoping shorts caption positioning to avoid subtitle glitches on regular watch.
• fix unsubscribe reliability by normalizing channel URLs and handling http/https variants so unsubscription and subscription state stay consistent.

Included Commits

• 2e97bcb fix: normalize channel URLs for unsubscribe consistency
• 14a6e0b refactor: apply theme tokens across routes and settings
• e48a814 refactor: migrate shared components to semantic theme tokens
• ac2b504 refactor: align admin and watch surfaces to theme tokens
• c874533 fix: restore watch mobile comments and stable subtitles
• 3082f32 feat: add persisted navbar theme toggle and runtime tokens

Validation

• bun run check
• bun run sherif
• bun run knip
• bun run build