Add classification blocks to marketplace entries

[jakemmarsh]

Adds a classification object to each of the 13 entries in .claude-plugin/marketplace.json so Claude's plugin directory can place these plugins into browse categories instead of leaving them uncategorized.

Shape — every key is optional; values come from a closed vocabulary and anything outside it is ignored server-side, never rejected:

"classification": {
  "object_acted_on": ["papers-articles", "data"],  // what the plugin works on (multi)
  "work_department": "finance",                    // team it's for
  "industry": "health-life-sciences",              // vertical, if any
  "life_area": "research",                         // personal-use area, if any
  "subject": "medicine"                            // subject matter, if any
}

Compatibility — purely additive. Clients that don't know the key ignore it (the marketplace entry schema is non-strict), and the file is otherwise semantically unchanged (verified by round-tripping the JSON with the new key removed).

Values are a first pass from each entry's own name/description — corrections welcome inline. Going forward, new entries should carry a classification block.

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[jakemmarsh]

I have read the CLA Document and I hereby sign the CLA

[jakemmarsh]

Closing — categories for these plugins are now derived server-side, so hand-authored classification blocks in the marketplace file are no longer needed. The server still honors an authored block if we ever want to pin one explicitly.