feat: add light theme

[triesmon]

Description

Adds a basic light theme with a toggle in the user menu.

The selected theme is saved in localStorage instead of user settings. This allows per-device flexibility that accessibility requiring users might desire. The argument for maintaining light mode is that users with visual impairments depend on and expect an experience consistent with other websites because they've tuned their accessibility settings to help with websites that are typically in light mode. See seerr-team#1793

I also added light versions of the Seerr wordmark logos so they stay readable on light backgrounds without changing the icon colors.

How Has This Been Tested?

• Ran pnpm lint
• Ran pnpm i18n:extract
• Ran pnpm build
• Ran pnpm test
• Manually checked light/dark theme switching in Chrome and Firefox
• Manually checked theme persistence after reload
• Manually checked the sidebar logo, title text, and title card overlay in light mode

Screenshots / Logs (if applicable)

N/A

Checklist:

• I have read and followed the contribution guidelines.
• Disclosed any use of AI (see our policy)
• I have updated the documentation accordingly. N/A - no docs changes needed.
• All new and existing tests passed.
• Successful build pnpm build
• Translation keys pnpm i18n:extract
• Database migration (if required). N/A - no database changes.

AI disclosure: I used AI to help implement and test this change, then reviewed the changes myself.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Replace the alpha placeholder before plugin CSS uses it

When .prose content is rendered, this helper makes theme('colors.*') return strings containing <alpha-value>; the typography extension below uses those raw theme values directly, so the generated .prose declarations contain invalid colors like rgb(var(...) / <alpha-value>) and browsers drop them. Utility classes still get the placeholder substituted, but plugin CSS needs a concrete alpha value or separate non-placeholder color tokens; this affects issue comments/descriptions and release notes that use prose.

Useful? React with 👍 / 👎.

[chatgpt-codex-connector]

Preserve the logo link name in light mode

When the light theme is active, CSS hides .seerr-logo-dark and shows .seerr-logo-light, but the visible image is explicitly empty and aria-hidden. The sidebar/login logo links then have no accessible name in light mode for screen reader users; give the light asset the same alt text, or only hide the inactive asset from assistive tech.

Useful? React with 👍 / 👎.