feat(skills): make skill scripts self-executing with uv hashbang

The Python scripts in mpi-pptx-translate, mpi-pdf-to-docx-conversion, and
mpi-chinese-text-normalize previously required users to type
manually. That is easy to forget and adds friction every time the skill runs.

Switch all four scripts to a  shebang,
so they can be invoked directly: . The
 PEP 723 metadata blocks remain, so uv still installs the
dependencies automatically. Also made the scripts executable and updated
their usage messages and SKILL.md instructions to match the direct-execution
style.

skills/mpi-chinese-text-normalize/SKILL.md

@@ -1,7 +1,7 @@
 ---
 name: mpi-chinese-text-normalize
 description: Normalize Chinese markdown files by removing extraneous mid-sentence line breaks from fixed-width exports while preserving TOC structures, section headers, and intentional paragraph breaks. Do not use for English prose, wiki-link index files, or mixed CJK/English documents without manual review.
-compatibility: Requires Python 3.9+ and uv. The script uses only the standard library.
+compatibility: Requires Python 3.9+ and uv. The script's shebang invokes `uv run --script`; it uses only the standard library.
 ---
 
 When Chinese text has hard line breaks at a fixed width (~20-25 chars) — common in PDF exports, OCR output, or poorly-converted documents — use this skill to join them into flowing paragraphs.
@@ -14,13 +14,13 @@ When Chinese text has hard line breaks at a fixed width (~20-25 chars) — commo
 
 ## Approach
 
-Run with `uv`:
+Run the script directly:
 
 ```bash
-uv run skills/mpi-chinese-text-normalize/scripts/normalize_breaks.py <directory>
+skills/mpi-chinese-text-normalize/scripts/normalize_breaks.py <directory>
 ```
 
-It processes all `.md` files in the directory.
+The shebang invokes `uv run --script`. It processes all `.md` files in the directory.
 
 The script handles three file patterns: