Unify input and container styling to glass design

[rogerdigital]

Summary

Unifies the previously inconsistent input and container styling across the app to a single glass design (translucent light-gray background, no border by default, subtle border on focus), using the custom-prompt textarea as the reference standard.

1. Unify form inputs to glass style

Three different "boxed input" styles were coexisting (white surface + border + focus ring vs. glass). All boxed inputs now use the glass style:

• promptTextarea (reference): fixed a focus flicker caused by border toggling from none to 1px solid — now uses a transparent border that stays constant.
• Settings fieldInput/fieldTextarea: white bg + border + focus ring → glass
• PublishChecklist titleInput/contentArea: surface white bg → glass
• TemplatePicker saveInput: surface white bg → glass

Writing-canvas inputs (title/body/immersive title) keep their borderless design.

2. Apply glass to editor/preview/publish containers

• editorCard (editor outer frame): surface white bg + shadow → glass; inner editorWrap reverted to transparent to let the outer glass show through.
• Preview area: phone frame / top bar / content area unified to glass; article content area keeps white for paper-reading effect.
• publishPanel: surface white bg + shadow → glass.
• Toolbar: background aligned with the editor input area (transparent), keeping the light top/bottom separator lines.

3. Layout refinements

• Publish checklist step 2: platform check cards (boxed cards with bg/border/radius) → flat list (bottom separator lines).
• Platform selector: heavy white pill chips → flat glass chips; selected state uses a light glass bg + bold text (removed the bottom indicator line, lightened the selected bg).

Verification

• `pnpm build` passes
• `pnpm lint` passes (lint-staged: prettier + eslint)

Out of scope

Cards/panels used as structural containers (settings connection cards, field groupings) are intentionally left with their own border — they serve a different visual role (container/grouping) than inputs (interactive controls).