refactor: consolidate loading/error states and extract instance actions hook

Frontend:
- Create reusable DataStates components (LoadingState, ErrorState, EmptyState)
- Refactor 12 pages to use shared state components instead of inline JSX
- Extract useInstanceActions hook to eliminate session action duplication
- Update dashboard and sessions pages to use shared hook

OpenSpec:
- Archive completed mobile-app-usability change (44/44 tasks)
- Archive completed add-config-profiles change (15/15 tasks)

Quality: TypeScript check passes, production build succeeds

openspec/changes/archive/2026-05-25-mobile-app-usability/specs/mobile-navigation/spec.md

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+## ADDED Requirements
+
+### Requirement: Mobile Bottom Navigation
+The system SHALL display a bottom tab bar for navigation on mobile viewports (width < 768px).
+
+#### Scenario: Mobile viewport shows bottom nav
+- **WHEN** the app is viewed on a device with width less than 768px
+- **THEN** a bottom tab bar is displayed at the bottom of the screen
+- **AND** it contains tabs for: Home, Projects, Sessions, Tools, Settings
+- **AND** the desktop sidebar navigation is hidden
+
+#### Scenario: Bottom nav tab selection
+- **WHEN** user taps a tab in the bottom navigation
+- **THEN** the app navigates to the corresponding route
+- **AND** the selected tab shows an active state
+
+#### Scenario: Bottom nav session badge
+- **GIVEN** the user has active sessions
+- **WHEN** viewing the bottom navigation
+- **THEN** the Sessions tab displays a badge with the active session count
+
+#### Scenario: Desktop viewport shows sidebar
+- **WHEN** the app is viewed on a device with width 768px or greater
+- **THEN** the desktop sidebar navigation is displayed
+- **AND** the bottom tab bar is hidden
+
+### Requirement: Safe Area Support
+The system SHALL account for mobile safe areas (notch, home indicator) in the bottom navigation.
+
+#### Scenario: iPhone with home indicator
+- **GIVEN** an iPhone with a home indicator
+- **WHEN** the bottom navigation is displayed
+- **THEN** it includes additional padding to avoid the home indicator
+- **AND** all navigation tabs remain fully tappable