refactor: reorganize skills into sub-categories

The skills directory was getting disorganized — mlops alone had 40
skills in a flat list, and 12 categories were singletons with just
one skill each.

Code change:
- prompt_builder.py: Support sub-categories in skill scanner.
  skills/mlops/training/axolotl/SKILL.md now shows as category
  'mlops/training' instead of just 'mlops'. Backwards-compatible
  with existing flat structure.

Split mlops (40 skills) into 7 sub-categories:
- mlops/training (12): accelerate, axolotl, flash-attention,
  grpo-rl-training, peft, pytorch-fsdp, pytorch-lightning,
  simpo, slime, torchtitan, trl-fine-tuning, unsloth
- mlops/inference (8): gguf, guidance, instructor, llama-cpp,
  obliteratus, outlines, tensorrt-llm, vllm
- mlops/models (6): audiocraft, clip, llava, segment-anything,
  stable-diffusion, whisper
- mlops/vector-databases (4): chroma, faiss, pinecone, qdrant
- mlops/evaluation (5): huggingface-tokenizers,
  lm-evaluation-harness, nemo-curator, saelens, weights-and-biases
- mlops/cloud (2): lambda-labs, modal
- mlops/research (1): dspy

Merged singleton categories:
- gifs → media (gif-search joins youtube-content)
- music-creation → media (heartmula, songsee)
- diagramming → creative (excalidraw joins ascii-art)
- ocr-and-documents → productivity
- domain → research (domain-intel)
- feeds → research (blogwatcher)
- market-data → research (polymarket)

Fixed misplaced skills:
- mlops/code-review → software-development (not ML-specific)
- mlops/ml-paper-writing → research (academic writing)

Added DESCRIPTION.md files for all new/updated categories.

skills/research/ml-paper-writing/templates/icml2026/algorithm.sty

@@ -0,0 +1,79 @@
+% ALGORITHM STYLE -- Released 8 April 1996
+%    for LaTeX-2e
+% Copyright -- 1994 Peter Williams
+% E-mail Peter.Williams@dsto.defence.gov.au
+\NeedsTeXFormat{LaTeX2e}
+\ProvidesPackage{algorithm}
+\typeout{Document Style `algorithm' - floating environment}
+
+\RequirePackage{float}
+\RequirePackage{ifthen}
+\newcommand{\ALG@within}{nothing}
+\newboolean{ALG@within}
+\setboolean{ALG@within}{false}
+\newcommand{\ALG@floatstyle}{ruled}
+\newcommand{\ALG@name}{Algorithm}
+\newcommand{\listalgorithmname}{List of \ALG@name s}
+
+% Declare Options
+% first appearance
+\DeclareOption{plain}{
+  \renewcommand{\ALG@floatstyle}{plain}
+}
+\DeclareOption{ruled}{
+  \renewcommand{\ALG@floatstyle}{ruled}
+}
+\DeclareOption{boxed}{
+  \renewcommand{\ALG@floatstyle}{boxed}
+}
+% then numbering convention
+\DeclareOption{part}{
+  \renewcommand{\ALG@within}{part}
+  \setboolean{ALG@within}{true}
+}
+\DeclareOption{chapter}{
+  \renewcommand{\ALG@within}{chapter}
+  \setboolean{ALG@within}{true}
+}
+\DeclareOption{section}{
+  \renewcommand{\ALG@within}{section}
+  \setboolean{ALG@within}{true}
+}
+\DeclareOption{subsection}{
+  \renewcommand{\ALG@within}{subsection}
+  \setboolean{ALG@within}{true}
+}
+\DeclareOption{subsubsection}{
+  \renewcommand{\ALG@within}{subsubsection}
+  \setboolean{ALG@within}{true}
+}
+\DeclareOption{nothing}{
+  \renewcommand{\ALG@within}{nothing}
+  \setboolean{ALG@within}{true}
+}
+\DeclareOption*{\edef\ALG@name{\CurrentOption}}
+
+% ALGORITHM
+%
+\ProcessOptions
+\floatstyle{\ALG@floatstyle}
+\ifthenelse{\boolean{ALG@within}}{
+  \ifthenelse{\equal{\ALG@within}{part}}
+     {\newfloat{algorithm}{htbp}{loa}[part]}{}
+  \ifthenelse{\equal{\ALG@within}{chapter}}
+     {\newfloat{algorithm}{htbp}{loa}[chapter]}{}
+  \ifthenelse{\equal{\ALG@within}{section}}
+     {\newfloat{algorithm}{htbp}{loa}[section]}{}
+  \ifthenelse{\equal{\ALG@within}{subsection}}
+     {\newfloat{algorithm}{htbp}{loa}[subsection]}{}
+  \ifthenelse{\equal{\ALG@within}{subsubsection}}
+     {\newfloat{algorithm}{htbp}{loa}[subsubsection]}{}
+  \ifthenelse{\equal{\ALG@within}{nothing}}
+     {\newfloat{algorithm}{htbp}{loa}}{}
+}{
+  \newfloat{algorithm}{htbp}{loa}
+}
+\floatname{algorithm}{\ALG@name}
+
+\newcommand{\listofalgorithms}{\listof{algorithm}{\listalgorithmname}}
+