feat: add session list overhaul proposal

- Add proposal for unified session list components
- Add design doc with component architecture
- Add specs for SessionCard and SessionList requirements
- Add implementation tasks

Refs: session-list-overhaul

openspec/changes/session-list-overhaul/design.md

@@ -0,0 +1,60 @@
+## Context
+
+The current session list implementation duplicates rendering logic across `dashboard.tsx` and `sessions.tsx`. Both pages fetch the same data, apply similar filtering (active vs recent/stopped), and render session cards with inconsistent styling and controls. The dashboard has a compact grid view while the sessions page has a list view, but neither provides all control actions (open, stop, start, delete) in a consistent way.
+
+## Goals / Non-Goals
+
+**Goals:**
+- Unified session card component with all control actions visible and accessible
+- Unified session list component that handles filtering, grouping, and empty states
+- Consistent visual design across dashboard and sessions pages
+- Clear status indicators (running, stopped, error, building, etc.)
+- Project/repository context visible on each card
+- Responsive layout that works on mobile and desktop
+
+**Non-Goals:**
+- No API changes
+- No new session management features (just better UI for existing ones)
+- No changes to session creation flow
+- No real-time updates beyond existing polling
+
+## Decisions
+
+**Decision: Two levels of components**
+- `SessionCard`: Individual session display with actions
+- `SessionList`: Container that handles grouping and layout
+This allows the dashboard to use `SessionList` directly while the sessions page can add additional filtering/controls around it.
+
+**Decision: Card-based layout over table**
+Cards provide better mobile experience and can show richer information (project context, tool icon, status badge). Tables are harder to make responsive.
+
+**Decision: Inline actions on cards**
+Each card shows primary action (Open for running, Start for stopped) and secondary actions in a dropdown or secondary button row. This matches the existing dashboard pattern but makes it consistent.
+
+**Decision: Status colors**
+- Running: green
+- Building/Starting/Probing: yellow/amber
+- Stopped: gray
+- Error: red
+- Unhealthy: orange
+
+## Risks / Trade-offs
+
+**Risk: Breaking existing dashboard layout**
+→ Mitigation: Keep the same grid layout structure, just swap the inner rendering to use SessionCard
+
+**Risk: Mobile experience with many action buttons**
+→ Mitigation: Use icon buttons on mobile, text buttons on desktop. Collapse secondary actions into a "..." menu.
+
+## Migration Plan
+
+1. Create SessionCard and SessionList components
+2. Update dashboard.tsx to use SessionList
+3. Update sessions.tsx to use SessionList
+4. Remove old duplicated session rendering code
+5. Update styles
+6. Test both pages
+
+## Open Questions
+
+None