fix: improve swappable filesystem architecture

[AnishSarkar22]

Description

1. Sidebar local-folder UX polish

   • Added clearer tooltip feedback when users hit folder-add limits.
   • Introduced loading skeletons in DocumentsSidebar and LocalFilesystemBrowser.
   • Removed unused drag-and-drop code paths to simplify sidebar behavior.

2. Local filesystem root handling + performance improvements

   • Standardized root canonicalization and mount resolution across backend/desktop/web flow.
   • Increased supported local roots (up to 10), improved path normalization, and added settings caching.
   • Preserved incremental interaction behavior so local-folder UX stays stable during updates.

3. Search-space aware filesystem operations

   • Propagated searchSpaceId through desktop IPC/preload, web integration, and typings.
   • Ensures filesystem requests execute against the correct search-space context end-to-end.

4. Desktop/web code-splitting cleanup

   • Extracted DesktopLocalTabContent from DocumentsSidebar.
   • Reduces web bundle impact by isolating desktop-specific local tab logic.

5. Backend filesystem capability expansion

   • Added move and list_tree operations in filesystem middleware/local backends.
   • Removed cursor-based pagination and simplified traversal/path normalization behavior.

6. Real-time local tree sync

   • Added chokidar-based filesystem tree watcher in desktop.
   • Wired events through IPC/preload/web so UI updates when local folder contents change.

7. File opening + fallback naming consistency

   • Added support for configurable openable local text extensions.
   • Improved folder expansion-state persistence in local browser UI.
   • Standardized text fallback filename behavior to notes.md (removed extension inference).

8. Source editor defaults refinement

   • Adjusted line number display, disabled folding, and tuned whitespace rendering for a cleaner editing experience.

Motivation and Context

FIX #

Screenshots

API Changes

• This PR includes API changes

Change Type

• Bug fix
• New feature
• Performance improvement
• Refactoring
• Documentation
• Dependency/Build system
• Breaking change
• Other (specify):

Testing Performed

• Tested locally
• Manual/QA verification

Checklist

• Follows project coding standards and conventions
• Documentation updated as needed
• Dependencies updated as needed
• No lint/build errors or new warnings
• All relevant tests are passing

High-level PR Summary

This PR introduces significant architectural improvements to the swappable filesystem feature for local folder mode. The main changes include: adding two new filesystem tools (move_file and list_tree with cursor-based pagination) to the agent middleware, implementing per-search-space filesystem settings isolation in the desktop app, adding a real-time filesystem tree watcher using chokidar with safety polling and debouncing, overhauling the local filesystem browser UI with skeleton loading states, and improving path normalization and mount resolution across the stack. The changes enable better scalability for large directory trees, multi-space support, and a more responsive user experience with live filesystem monitoring.

⏱️ Estimated Review Time: 1-3 hours

💡 Review Order Suggestion

Order	File Path
1	surfsense_backend/app/agents/new_chat/middleware/filesystem.py
2	surfsense_backend/app/agents/new_chat/middleware/local_folder_backend.py
3	surfsense_backend/app/agents/new_chat/middleware/multi_root_local_folder_backend.py
4	surfsense_backend/tests/unit/middleware/test_filesystem_backends.py
5	surfsense_backend/tests/unit/middleware/test_multi_root_local_folder_backend.py
6	surfsense_desktop/src/modules/agent-filesystem.ts
7	surfsense_desktop/src/modules/agent-filesystem-tree-watcher.ts
8	surfsense_desktop/src/ipc/channels.ts
9	surfsense_desktop/src/ipc/handlers.ts
10	surfsense_desktop/src/preload.ts
11	surfsense_web/types/window.d.ts
12	surfsense_web/lib/agent-filesystem.ts
13	surfsense_web/components/editor-panel/editor-panel.tsx
14	surfsense_web/components/assistant-ui/markdown-text.tsx
15	surfsense_web/components/layout/ui/sidebar/LocalFilesystemBrowser.tsx
16	surfsense_web/components/layout/ui/sidebar/DesktopLocalTabContent.tsx
17	surfsense_web/components/layout/ui/sidebar/DocumentsSidebar.tsx
18	surfsense_web/app/dashboard/[search_space_id]/new-chat/[[...chat_id]]/page.tsx
19	surfsense_web/components/ui/tooltip.tsx

⚠️ Inconsistent Changes Detected

File Path	Warning
surfsense_web/components/ui/tooltip.tsx	Changes tooltip behavior from mobile detection to hover-capability detection. While this improves UX, it appears to be a general UI enhancement rather than directly related to the filesystem architecture improvements.

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