refactor(skills): align MPI skills with Agent Skills best practices

The skill metadata had drifted: every SKILL.md name field lacked the
mpi- prefix, contradicting the directory names and the Agent Skills
specification. Descriptions were also missing negative triggers, making
it easy for the agent to load the wrong skill.

Rewrote the pdf-to-docx skill to follow progressive disclosure: the main
SKILL.md dropped from 318 lines to 80, with detailed code examples moved
to on-demand references. Added uv run instructions and /// script PEP 723
metadata so dependencies are declared inline and installed automatically.
Fixed the pptx skill's script paths and added CLI usage messages to both
pptx scripts and the normalize script.

Removed the empty self-review directory that was superseded by the unified
translation-review skill.

skills/mpi-translation-review/SKILL.md

@@ -1,13 +1,9 @@
 ---
-name: translation-review
+name: mpi-translation-review
 description: |
-  Unified review skill for Chinese-English Buddhist/Dharma translations.
-  Supports two modes:
-  - **self**: You translated the text. Edit target.dj directly.
-  - **other**: Someone else translated. Write review-comments.dj, do not edit target.dj.
-  What to review is identical in both modes — the same detection rules,
-  editorial standards, and terminology checks. Only the action differs: self
-  mode applies fixes directly; other mode records them for the translator.
+  Unified review skill for Chinese-English Buddhist/Dharma translations in djot format.
+  Use in self mode to edit your own target.dj, or in other mode to write review-comments.dj for a peer translator.
+  Do not use for non-djot formats or for non-Buddhist texts.
 ---
 
 # Translation Review (unified)