RustBox 0.0.6 source release

Runtime/source model:
- one root Cargo package
- src/ Rust application code
- src/web/ RustBox-owned embedded browser UI
- migrations/ SQLite migrations
- no TypeScript/React/Next.js/Node.js/Bun build
- ManageSieve TLS/STARTTLS/explicit insecure transport option
- native systemd packaging

Oxi tracking:
- UPSTREAM_BASE stores consumed Oxi revision
- scripts/setup-upstream.sh configures upstream-oxi
- scripts/oxi-status.sh reports upstream changes
- scripts/sync-upstream.sh maps the cumulative Oxi backend delta into flat RustBox paths
- scripts/finish-upstream.sh advances UPSTREAM_BASE only after explicit upstream review/build validation
- scripts/oxi-port-commit.sh maps a selected Oxi backend commit without advancing the baseline
- Oxi frontend changes are reviewed and manually ported to src/web/
- docs/UI.md documents the browser UI/build conventions

Current 0.0.6 release additions:
- attachment left-click defaults to safe in-app preview for supported types
- attachment right-click exposes explicit Preview and Download actions
- oversized preview attempts offer direct download instead of ending with a warning
- Polish composer, reader toolbar and per-message context-menu translation pass
- grouped reader message details menu for headers/source and transfer menu for move/copy
- compact composer format selector moved to the lower-right opposite Send/Cancel
- mobile layout reliability pass for settings, source/header/calendar dialogs and narrow toolbars
- fixed Sieve visual-editor checkbox alignment and mobile single-column rule controls
- tap/keyboard expansion for full sender/recipient address details in the reader
- persistent IMAP quota progress above the sidebar IMAP/version footer
- global TOML `default_theme` for light/dark mode and `default_interface_skin` for login + account-wide default interface styling
- Gmail-, Proton-, Zoho- and Outlook-inspired interface profiles plus Minimal
- expanded Polish localization, including scoped dialog/settings text and common attributes
- JavaScript source split into functional `src/web/js/` modules and assembled by Cargo build.rs
- Interface style selector expanded to RustBox custom, Roundcube Classic/Larry/Elastic, Clean, Graphite, High contrast, Gmail-, Proton-, Zoho-, Outlook-inspired and Minimal
- legacy Compact/Balanced/Comfortable/Reading appearance cards removed
- persisted special folders and mailbox behavior preferences
- bulk IMAP actions, copy/move, folder mark-all-read/empty, message-to-folder drag/drop
- HTML/plain/Markdown composer modes, CID inline images and expanded identity/signature rules
- advanced/saved search, tags, contact groups, visual Sieve/vacation builder
- IMAP IDLE/WebSocket refresh, desktop notifications and DND
- IMAP capabilities diagnostics and multi-account browser session UI
- RFC822 .eml download/import, List-Unsubscribe handling and RFC 8058 one-click HTTPS unsubscribe
- expanded contacts with multiple e-mails/phones/addresses, vCard profile fields, duplicate merge and validated PNG/JPEG/WebP photos
- calendar Month/Week/Day/Agenda views, richer event metadata and ICS import/export
- search-index status/rebuild, IMAP reconnect diagnostics and live cross-browser session revoke UI
- 45 contiguous SQLite migrations wired sequentially; V042 adds per-user trusted senders, V043 saved responses, V044 interface skins and V045 saved-response format
- safe Undo for resolvable IMAP MOVE actions and select-all across complete cached search results
- exact-token thread matching and expanded keyboard selection/navigation shortcuts
- in-app attachment preview, clipboard CID image paste and upload progress
- separate 10 MiB per-file attachment limit and 50 MiB final RFC822/MIME message limit with pre-SMTP exact byte validation and composer size estimate
- recoverable drafts with browser emergency snapshots and throttled IMAP Drafts snapshots
- outgoing priority and MDN/read-receipt draft/send options with pre-SMTP mailbox validation
- expanded Sieve visual rules: nested three-condition grouping, two actions, managed reordering, backup/restore, active overwrite guard and optional date-scheduled vacation
- spam destination default plus per-account override, pre-pagination flagged-first sorting with per-folder overrides, and subtle flagged-row markers
- direct ManageSieve quick-filter wizard with validation/save/activation and advanced-editor handoff
- unread browser/app badge updates and a public local-storage readiness endpoint
- inline image editing with display sizing, alignment, crop/cut preview and CID cleanup
- dedicated Composing settings for format, autosave interval, default priority, MDN and attachment reminder
- corrected Settings header/content grid for short panels and scroll-safe navigation

Validation note:
- JavaScript, JSON, TOML, SVG, shell syntax, UI selector/icon integrity and SQLite migrations were validated in the release environment.
- A full cargo build/test was not executed in this environment because cargo/rustc are not installed; run ./dev.sh or cargo test on a Rust toolchain host before deployment.

0.0.6 additions:
- mobile reader action and attachment fixes
- WebSocket heartbeat, reconnect backoff, watchdog, resync, dedupe and fallback polling
- reliable live new-message refresh and unread reconciliation
- notification click-through to the newest message when UID is available
- full-screen message reader with context-menu entry, Escape, history and deep links
- composer-only upload progress with duplicate and cancellation safeguards
- source-code comment removal and regression contracts