docs: expand README with full ROS2 Jazzy install + runtime instructions

Previously the README on ros2_dev linked to the ROS1 wiki for all
install, docker, simulation, SLAM, and LIDAR-only flow details. Mirror
those wiki pages into the README directly (adapted for ROS2 Jazzy) so
users on this branch no longer need to translate ROS1 wiki instructions
in their head.

The experimental [!NOTE] banner at the top is preserved byte-for-byte,
as is the docs/falcon4-compressed.jpg hero image, the short project
description, the seven docker-build CI badges, the videos, the
contributing / citation / acknowledgement sections, and the high-level
code-structure image.

New / rewritten sections (17 top-level headers added):

- Table of contents (new, covers all sections below)
- System requirements — Ubuntu 24.04, ROS2 Jazzy, Python 3.12, GPU
  only required for SLAM / VIO inference.
- Install ROS2 Jazzy — apt install pointing at the official
  docs.ros.org jazzy instructions.
- Build from source — full step-by-step: mkdir workspace, git clone
  --branch ros2_dev, vcs import < external_all.yaml (with a clear
  caveat that the external yamls are still ROS1-only TODOs), rosdep
  install, apt install libspdlog-dev, colcon build --symlink-install
  --cmake-args -DCMAKE_BUILD_TYPE=Release, source install/setup.bash.
- Use docker (recommended) — pull the
  kumarrobotics/autonomy:base-jazzy placeholder tag, run the
  autonomy_core/*/docker/run.sh scripts, build inside with colcon,
  source install/setup.bash. Mirrors the wiki "Using Docker" page
  adapted for the -jazzy tag suffix.
- Converting ROS1 bags to ROS2 — short subsection documenting
  `pip install rosbags` + `rosbags-convert --src input.bag
  --dst output_bag_dir/`.
- Run Gazebo simulation — mirror of the wiki Gazebo-Simulation-Setup
  steps, every `roslaunch gazebo_utils x.launch` rewritten as
  `ros2 launch gazebo_utils x.launch.py`. Explicit note that Gazebo
  Harmonic on Jazzy uses ros_gz_* bindings and the user may need
  `ros-jazzy-ros-gz` + `ros-jazzy-ros-gz-sim`.
- Run with SLAM (LIDAR + VIO) — 5-terminal bring-up sequence
  reconstructed from the actual .launch.py files on this branch
  (the wiki page had no command blocks, only an architecture
  description). Marked with an italic caveat that the exact ordering
  is unverified end-to-end.
- Run LIDAR-only autonomous flight — mirrors the wiki page. Uses
  drivers_for_faster_lio.launch.py, faster_lio_for_autonomy.launch.py,
  full_autonomy.launch.py in order.
- Run full coverage experiments — short mirror of the wiki page,
  notes that the external_coverage_planner.yaml vcs import still
  resolves to ROS1-only packages.
- Real-robot deployment — high-level pointer section noting that
  full real-robot deployment needs Pixhawk + NUC + Ouster + OVC3
  + VN-100 + Falcon4, and that the hardware setup / calibration
  / preflight / WiFi / network pages in the ROS1 wiki have not yet
  been ported to ROS2.
- Troubleshooting — short list of the common ROS2 port issues:
  colcon build fails on an external package (look at the
  external_*.yaml TODOs), rosdep can't resolve a key, ros2 launch
  can't find a launch file because the workspace overlay is not
  sourced, Gazebo Harmonic bridge missing.
- High-level code structure (existing section, kept unchanged).
- Videos (existing section, kept unchanged).
- Contributing (existing section, kept unchanged).
- Citation (existing section, kept unchanged).
- Acknowledgement (existing section, kept unchanged).
- License (existing section, kept unchanged).

Italic "Translated from the ROS1 wiki, not yet verified on a ROS2
Jazzy workspace" notes are attached to each section whose commands
are reconstructed rather than directly copied from a wiki command
block. The SLAM bring-up sequence is the largest unverified area
because the wiki's "Running with SLAM" page contained no command
examples at all.

README grew from 107 lines to 460 lines.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: XuRobotics