Cleanup Slash Command & Agent

[dannysmith]

This is essentially a more advanced version of tdn doctor Except it's intended to go into the contents and structure of all of the files. The command should:

1. Run tdn context and tdn doctor
2. Spawn some custom subagents to explore all task, project and area files and report back on recommended changes/fixes.

We're looking for:

This kinda thing

• Basic stuff: malformed or incorrect frontmatter, titles which should be reworded/improved, random files, "empty" tasks etc which shouldn't be there. Duplicate tasks/projects etc.
• Slightly-less-basic stuff which requires an understanding of context: statuses, dates etc which need updating. Tasks which should be archived. Stale or forgotten tasks etc. Accidentally orphaned tasks/projects etc.
• Thinky stuff: Tasks which should be split or combined. Stuff in project or area bodies which should maybe be turned into tasks or projects. Related tasks which should maybe be globbed into a project.
• Area and Project body content which is outdated, or is new and hasn't had goals/descriptions etc added. Etc.

This command should be careful, it doesn't accidentally turn into a full review. the job here is taking the information which is already in the system and cleaning it up and reorganizing it. So that nothing is incorrect. it shouldn't be adding a whole load of invented information. It shouldn't be inventing random tasks and creating them without user input. And it certainly shouldn't be doing any extensive planning.