feat(ui): redesign Explorer, toolbar, icons, and localization

[ThisIs-Developer]

Summary

• Adds a closable Explorer with workspace, folder, file, drag-and-drop, favorites, multi-selection, context-menu, secret-workspace, and background-import workflows.
• Preserves documents when tabs close, adds contextual close commands, and supports synchronized two-document split workflows.
• Reorganizes the Markdown toolbar and standardizes the interface on a locally bundled Lucide icon subset with 1.5px strokes, while retaining the Bootstrap GitHub brand mark.
• Refines the header, overlays, empty-document experience, status bar, mobile workspace drawer, desktop resources, and application-wide localization.
• Organizes the repository into clear web asset, desktop source, build-script, generated-resource, documentation, worker, and platform-integration areas.

Codebase organization

• Groups deployable browser assets under assets/css, assets/js, assets/images, assets/i18n, assets/examples, and assets/licenses.
• Adds assets/README.md as a concise ownership map for future contributors.
• Keeps platform-required entrypoints and configuration at the repository root while preserving the existing functions, workers, scripts, wiki, and locales boundaries.
• Moves desktop-only source to desktop-app/src, type declarations to desktop-app/types, and build utilities to desktop-app/scripts.
• Treats desktop-app/resources as generated output and removes committed copies of the web script, worker, stylesheet, images, and generated HTML.
• Updates HTML, worker resolution, service-worker caching, manifest icons, locale generation, Docker packaging, Neutralino configuration, package scripts, and documentation to the canonical paths.
• Gives the desktop Dockerfile its standard Dockerfile-specific ignore file and keeps the relocated welcome example in both web and container build contexts.

Complete interface localization

• Adds versioned catalogs for English, Simplified Chinese, Traditional Chinese, Japanese, Korean, Portuguese, Spanish, French, German, Russian, Italian, Turkish, Polish, and Ukrainian.
• Expands coverage from 702 to 1,029 interface strings per locale, including runtime-only dialogs, context menus, Explorer states, editor placeholders, review/import/share notices, PDF/image progress, validation feedback, hover titles, and ARIA labels.
• Fixes every reported mixed-language state: Secret Workspace setup and lock actions, text-case labels, text direction, Reset confirmation, editor placeholder, Markdown alerts, Recent/Favorites empty states, PDF progress, and GitHub file selection.
• Keeps Aa, AA, aa, heading symbols, and the match-case glyph as non-translatable control symbols; toolbar icons and their layout are unchanged.
• Localizes dynamic counts and time units without leaking English words inside translated sentences.
• Translates newly created and dynamically updated UI through a scoped MutationObserver without re-rendering the editor.
• Keeps Markdown source, rendered preview content, user file names, user comments, GitHub tree names, and language autonyms outside automatic translation.
• Protects Markdown Viewer and Markdown from incorrect literal translation and applies curated Korean, Simplified Chinese, Traditional Chinese, and German UI terminology.
• Loads only the selected locale, caches it in memory, and retains offline desktop/service-worker support.
• Extends the catalog generator to discover dynamic UI labels, update catalogs incrementally, remove stale keys, and preserve interpolation placeholders.

Explorer, tabs, imports, and toolbar

• Workspace and folder rows toggle from the full row with pointer, Enter, or Space input while maintaining aria-expanded.
• Files and folders support normal, Ctrl/Command, and Shift selection, keyboard context menus, safe bulk actions, and confirmed bulk deletion.
• Removes redundant hover-only add controls and the redundant Open action from folder menus.
• Creates/reuses a repository-named Workspace folder for GitHub imports, closes the import dialog on submission, and reports background progress in a compact toast.
• New, Export, formatting, and application dropdowns share one visual and interaction system.
• Document utilities, review controls, view modes, formatting, insert tools, Diagram & More, Share, Live Share, and Export retain their behavior.

Responsive UI and mobile follow-up

• Replaces the floating mobile menu with a compact full-height workspace drawer using View, Document tools, and Actions hierarchy.
• Keeps one mobile accordion section open, resets accordion state after dismissal, traps focus, restores the trigger, and supports backdrop/Escape/breakpoint closing.
• Keeps mobile Sync, Copy, Review, Theme, Language, Private mode, and Reset synchronized with their desktop actions.
• Gives disabled mobile actions clear visual and semantic states when no document is open.
• Keeps the mobile tab strip, tab items, and Markdown formatting toolbar at the same 40px height.
• Preserves the no-document guard and shared compact modal system across light/dark responsive layouts.

Icon system

• Uses a local, dependency-free Lucide CSS-mask subset at a consistent 1.5px stroke with shared size and color tokens.
• Live Share uses Lucide radio; Private mode uses hat-glasses; Reset workspace uses power.
• The Bootstrap GitHub mark remains the sole brand-icon exception and its license is bundled locally.

Desktop build

• Generates the Neutralino resource tree from the canonical web assets and desktop-app/src/main.js instead of maintaining duplicate tracked copies.
• Copies all 14 locale catalogs into the offline desktop bundle.
• Keeps setup, preparation, and standalone build commands stable through the updated package scripts.
• Rebuilds seven standalone targets: Windows x64, macOS x64/arm64/universal, and Linux x64/arm64/armhf.

Validation

• Catalog integrity: 1,029 keys × 14 catalogs, zero missing values, zero mismatched keys, and zero broken {{…}} placeholders.
• Korean/Chinese screenshot-state browser checks: 3 passed.
• Existing responsive/sidebar regression suites: 16 passed.
• Core startup/editor/worker/import browser regression suite: 9 passed.
• Static UI translation coverage audit: zero untranslated catalogued text nodes, placeholders, titles, or ARIA labels.
• node --check assets/js/app.js — passed.
• node --check assets/js/preview-worker.js — passed.
• node --check desktop-app/scripts/*.js — passed.
• npm run build — passed.
• npm run setup in desktop-app — generated resources match their source files.
• npm run build in desktop-app — seven standalone targets generated successfully after the restructure.
• git diff --check — passed.

Commit messages

Conventional commit style is used throughout this pull request (feat, fix, style, refactor, and chore).

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Project	Deployment	Actions	Updated (UTC)
markdown-viwer	Ready	Preview, Comment	Jul 19, 2026 8:59pm

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[ThisIs-Developer]

Superseded by #221 after the feature branch was renamed to codex/ui-explorer-toolbar-localization.