UI redesign: popover feed, settings, onboarding + bug fixes

[trankhacvy]

Summary

• Rebuilt the popover feed with a flat deployment list, account group headers, and a new FilterBar (account picker + project filter with search, checkboxes, and status dots)
• Redesigned the popover header (health pill with pulse), footer (live relative timestamp, "Checking…" on refresh, real interval from prefs), and all empty/loading/offline state screens
• Rewrote Settings tabs (General with polling/notification/shortcut controls, Accounts with health badges, About with version info) and the Onboarding flow (3-step wizard with Railway OAuth support)
• Added a dev_reset Tauri command (debug builds only) that wipes the store and OS keychain, wired to a two-step confirm UI in Settings; added a browser-based dev sandbox for UI iteration without running the desktop app
• Fixed window.confirm blocked in Tauri, decorations: true duplicate title bar, misaligned FilterBar icons, stuck "Checking…" on failed refresh, and Shift+Enter falling back to site URL instead of logs-only