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-session-management/spec.md

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+## ADDED Requirements
+
+### Requirement: Touch-Optimized Session Cards
+The system SHALL render session cards with touch-friendly layouts on mobile viewports.
+
+#### Scenario: Session card touch targets
+- **GIVEN** a session card displayed on mobile
+- **THEN** all interactive elements have a minimum height of 44px
+- **AND** action buttons have adequate spacing (minimum 8px between adjacent targets)
+
+#### Scenario: Session card action menu
+- **GIVEN** a session card on mobile
+- **WHEN** the user taps the actions menu button
+- **THEN** a sheet or dropdown appears with all available actions
+- **AND** the actions include: Open, Terminal, Stop/Start, Restart, Delete
+- **AND** tapping outside the menu closes it
+
+#### Scenario: Primary action visibility
+- **GIVEN** a running session card on mobile
+- **THEN** the primary action (Open or Terminal) remains visible as a prominent button
+- **AND** secondary actions are accessible through the actions menu
+
+### Requirement: Mobile Session Creation
+The system SHALL provide a mobile-optimized session creation flow.
+
+#### Scenario: Create session form on mobile
+- **GIVEN** the create session form on a mobile viewport
+- **THEN** all form fields stack vertically in a single column
+- **AND** each field has a minimum height of 44px
+- **AND** the form is scrollable if it exceeds the viewport height
+
+#### Scenario: Session creation loading state
+- **GIVEN** the user submits the create session form on mobile
+- **WHEN** the request is in progress
+- **THEN** a loading indicator is displayed
+- **AND** the submit button is disabled to prevent double-submission
+
+### Requirement: Mobile Session List
+The system SHALL display the session list optimized for mobile scrolling.
+
+#### Scenario: Session list scrolling
+- **GIVEN** multiple sessions on mobile
+- **THEN** the session list is vertically scrollable
+- **AND** each session card has adequate vertical spacing for touch selection
+- **AND** the list does not horizontally scroll
+
+#### Scenario: Empty state on mobile
+- **GIVEN** no active sessions on mobile
+- **THEN** the empty state is centered and readable on the viewport
+- **AND** the call-to-action button is prominent and tappable