feat: add notesmd-cli package and flake checks

- Add notesmd-cli package for Obsidian CLI interaction
- Add flake checks for package build verification
- Add documentation for notesmd-cli, sidecar, and td
- Update AGENTS.md to reference td instead of beads
- Format pkgs/default.nix with proper braces

docs/README.md

@@ -35,10 +35,13 @@ Documentation for all custom packages:
 - [mem0](./packages/mem0.md) - AI memory assistant with vector storage
 - [msty-studio](./packages/msty-studio.md) - Msty Studio application
 - [n8n](./packages/n8n.md) - Free and source-available fair-code licensed workflow automation tool
+- [notesmd-cli](./packages/notesmd-cli.md) - Obsidian CLI (Community) - Interact with Obsidian in the terminal
 - [opencode](./packages/opencode.md) - AI coding agent built for terminal
 - [pomodoro-timer](./packages/pomodoro-timer.md) - Pomodoro timer utility
 - [rofi-project-opener](./packages/rofi-project-opener.md) - Rofi-based project launcher with custom args
+- [sidecar](./packages/sidecar.md) - Companion tool for CLI agents with diffs, file trees, and task management
 - [stt-ptt](./packages/stt-ptt.md) - Push to Talk Speech to Text using Whisper
+- [td](./packages/td.md) - Minimalist CLI for tracking tasks across AI coding sessions
 - [tuxedo-backlight](./packages/tuxedo-backlight.md) - Backlight control for Tuxedo laptops
 - [zellij-ps](./packages/zellij-ps.md) - Project switcher for Zellij