[Feature] Archive stories with sidebar toggle

[realproject7]

Problem

Users accumulate stories over time but have no way to organize them. Old/completed stories clutter the sidebar alongside active ones.

Solution

Add an archive feature for stories that have structure.md (confirmed stories only — not untitled sessions).

Archive button

Located on the top-right of the terminal session tab (same position as the Cancel button for untitled sessions). Only visible for confirmed stories (those with structure.md).

┌─────────────────────────────────────────────┐
│ ● seoul-slowly ×                [Archive]   │
│─────────────────────────────────────────────│
│  Claude Code v2.1.92                        │

Clicking shows a confirmation: "Archive this story? You can restore it later."

On archive:

Move the story folder from ~/.plotlink-ows/stories/{name}/ to ~/.plotlink-ows/stories/.archived/{name}/. The .archived prefix hides it from the normal story scan.

Sidebar toggle

Replace the bottom area (where "+ New Story" used to be) with a "View Archives" toggle button.

NORMAL VIEW:
┌──────────────┐
│ Stories    2  │
│ [+ New Story]│
│              │
│ ▸ new-emp... │
│ ▸ seoul-s... │
│              │
│              │
│ [📦 Archives]│  ← bottom of sidebar
└──────────────┘

ARCHIVE VIEW:
┌──────────────┐
│ 📦 Archives 1│
│ [← Back]     │
│              │
│ ▸ old-story  │  
│   [Restore]  │  ← per-story restore button
│              │
└──────────────┘

Archive view behavior:

• Sidebar switches to show only archived stories
• Each archived story has a "Restore" button/action
• Restoring moves the folder back from .archived/ to stories/
• "← Back" returns to the normal stories view
• No terminal sessions for archived stories (read-only browse)

API endpoints:

• POST /api/stories/archive — body: { name } — moves to .archived/
• POST /api/stories/restore — body: { name } — moves back from .archived/
• GET /api/stories/archived — lists stories in .archived/

Files

• app/web/components/StoryBrowser.tsx — archive view toggle, restore buttons
• app/web/components/TerminalPanel.tsx — archive button on session tab
• app/web/components/StoriesPage.tsx — archive state management
• app/routes/stories.ts — archive/restore/list-archived endpoints

Acceptance Criteria

• Archive button on top-right of terminal for confirmed stories
• Confirmation popup before archiving
• Story folder moved to .archived/ subdirectory
• Archived story removed from main sidebar
• "Archives" toggle at bottom of sidebar
• Archive view shows archived stories with Restore button
• Restore moves story back to main stories list
• "← Back" returns to normal view
• Untitled sessions show Cancel button (not Archive)
• Only stories with structure.md can be archived