Rework mention of `manim init project` in quickstart guide

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The quickstart guide mentions project creation via `manim init project`, which leads to a somewhat different file and project structure than assumed below. This part should be reworked (or removed).

---

Original report:

#### Preliminaries

- [x ] I have followed the latest version of the
[installation instructions](https://docs.manim.community/en/stable/installation.html).
- [ x] I have checked the [installation FAQ](https://docs.manim.community/en/stable/faq/installation.html) and my problem is either not mentioned there,
or the solution given there does not help.

## Description of error
The quickstart guide differs from the downloaded default project and includes some other options not menitoned ("MovingCamera" and "Axes"?).

The class name has changed from "CreateCircle" to "DefaultTemplate", the python file is called `main.py` not `scene.py` as stated later in the guide, and there are more lines of code present.

Additionally, the rendered video is in low quality and zoomed in, so the edges of the shapes get cut off when animating. When rendering a test video with `checkhealth` the video is higher quality and scaled correctly.

## Installation logs

Checkhealth output

Python executable: /opt/homebrew/Cellar/manim/0.19.0/libexec/bin/python

Checking whether your installation of Manim Community is healthy...
- Checking whether manim is on your PATH ... PASSED
- Checking whether the executable belongs to manim ... PASSED
- Checking whether latex is available ... PASSED
- Checking whether dvisvgm is available ... PASSED

No problems detected, your installation seems healthy!

## System specifications

System Details

- OS: macOS Sequoia 15.4.1
- RAM: 24 GB
- Python version: 3.13.3
- Installed modules (hombrew):
```
==> Formulae
aom ghostscript libde265 libunistring node snappy
aribb24 giflib libdeflate libuv numpy speedtest-cli
asciiquarium glib libevent libvidstab oh-my-posh speex
berkeley-db@5 gmp libheif libvmaf openblas sqlite
boost gnutls libidn libvorbis opencore-amr srt
boost-python3 go libidn2 libvpx openexr svt-av1
brotli gobject-introspection libimagequant libx11 openjpeg tesseract
btop graphite2 liblqr libxau openssl@3 theora
c-ares harfbuzz libmicrohttpd libxcb opus unbound
c2048 highway libmpc libxdmcp p11-kit webp
ca-certificates icu4c@76 libnghttp2 libxext pango wifi-password
cairo icu4c@77 libogg libxrender pcre2 x264
certifi imagemagick libomp little-cms2 perl x265
cjson imath libpng lz4 pillow xorgproto
dav1d inih libraqm lzo pipx xsimd
exiv2 isl libraw m4 pixman xvid
fastfetch jasper librist mailsy pkgconf xz
ffmpeg jbig2dec libsamplerate manim py3cairo yt-dlp
flac jpeg-turbo libsndfile mbedtls pygobject3 zeromq
fontconfig jpeg-xl libsodium meson python@3.13 zimg
freetype lame libsoxr mpdecimal rav1e zstd
frei0r leptonica libssh mpfr readline
fribidi libarchive libtasn1 mpg123 rubberband
gcc libass libtiff ncurses scipy
gdbm libb2 libtool nettle sdl2
gettext libbluray libunibreak ninja shared-mime-info

==> Casks
wine-crossover youtube-music
```

LaTeX details

+ LaTeX distribution: MacTeX 2025
+ Installed LaTeX packages:
exceeded the output history for my terminal

## Additional comments

Start with the quickstart guide section that mentions `manim init project`, then compare its instructions with the generated default project structure, including `main.py` and `DefaultTemplate`. Rework or remove the conflicting project-creation guidance and ensure the subsequent examples match; the reported video-quality issue is separate from the documentation change.

Written by the indexing model from the issue text.