Replace session picker modal with instance welcome view

Transform the session picker from a modal into a comprehensive welcome screen that displays instance metadata, session history, and creation options. The new view provides full keyboard navigation, shows MCP server status, OpenCode binary path, and project information in a compact, space-efficient layout.

Key features:
- Instance metadata sidebar showing folder, project, VCS, version, binary path, MCP status, and server info
- Session list with keyboard navigation (↑↓, PgUp/PgDn, Home/End, Enter)
- Cmd+Enter shortcut to create new session from anywhere
- Compact design with efficient space usage
- Visual MCP server status indicators (running/stopped/error)
- Scrollable layout that keeps "New Session" section accessible

src/types/instance.ts

@@ -6,6 +6,27 @@ export interface LogEntry {
   message: string
 }
 
+export interface ProjectInfo {
+  id: string
+  worktree: string
+  vcs?: "git"
+  time: {
+    created: number
+    initialized?: number
+  }
+}
+
+export interface McpServerStatus {
+  name: string
+  status: "running" | "stopped" | "error"
+}
+
+export interface InstanceMetadata {
+  project?: ProjectInfo
+  mcpStatus?: unknown
+  version?: string
+}
+
 export interface Instance {
   id: string
   folder: string
@@ -15,4 +36,6 @@ export interface Instance {
   error?: string
   client: OpencodeClient | null
   logs: LogEntry[]
+  metadata?: InstanceMetadata
+  binaryPath?: string
 }