chore: 框架科学优化前的完整基线

在开始'设备契约层 + 目录重构 + 通止规装配'改造之前，先钉住当前可运行状态，
使后续任何删除/重构都可回退。

本基线包含：
- 现有 ROS 2 工作区全部源码（arm_application / arm_control / arm_bringup 等）
- 官方 flexiv_ros2 栈（含 flexiv_hardware / flexiv_controllers 等符号链接）
- 设备契约层 src/arm_interfaces（新增，46 项单测通过）
- devices/ 设备选型与品牌清单（新增）
- scripts/gen_site_example.py 与由它生成的 config/site.example.yaml

按 .gitignore 排除：build/ / install/ / log/ / config/site.yaml / 模型权重二进制。

config/fastdds_visual_servo.xml

@@ -0,0 +1,84 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<!--
+  FastDDS profile for visual-servo hard paths (Ubuntu 22.04 / Humble default RMW).
+
+  Use:
+    export FASTRTPS_DEFAULT_PROFILES_FILE=~/ros2/config/fastdds_visual_servo.xml
+    export RMW_IMPLEMENTATION=rmw_fastrtps_cpp
+
+  Goals:
+  - Prefer UDP unicast for low-latency control topics
+  - Shrink discovery / participant lease so late joiners do not stall 100 Hz
+  - Keep history shallow so subscribers never chase a backlog
+-->
+<profiles xmlns="http://www.eprosima.com/XMLSchemas/fastRTPS_Profiles">
+  <transport_descriptors>
+    <transport_descriptor>
+      <transport_id>udp_transport</transport_id>
+      <type>UDPv4</type>
+      <!-- Avoid shared-memory backlog stalls between heavy perception and servo -->
+      <maxMessageSize>65500</maxMessageSize>
+    </transport_descriptor>
+  </transport_descriptors>
+
+  <participant profile_name="visual_servo_participant" is_default_profile="true">
+    <rtps>
+      <userTransports>
+        <transport_id>udp_transport</transport_id>
+      </userTransports>
+      <useBuiltinTransports>false</useBuiltinTransports>
+      <builtin>
+        <discovery_config>
+          <!-- Faster discovery; reduce lease so dead peers drop quickly -->
+          <leaseDuration>
+            <sec>10</sec>
+            <nanosec>0</nanosec>
+          </leaseDuration>
+          <leaseAnnouncement>
+            <sec>3</sec>
+            <nanosec>0</nanosec>
+          </leaseAnnouncement>
+          <initialAnnouncements>
+            <count>5</count>
+            <period>
+              <sec>0</sec>
+              <nanosec>100000000</nanosec>
+            </period>
+          </initialAnnouncements>
+        </discovery_config>
+      </builtin>
+    </rtps>
+  </participant>
+
+  <!-- Perception image topics: BEST_EFFORT + KEEP_LAST (drop old frames) -->
+  <data_reader profile_name="sensor_best_effort">
+    <qos>
+      <reliability>
+        <kind>BEST_EFFORT</kind>
+      </reliability>
+      <history>
+        <kind>KEEP_LAST</kind>
+        <depth>5</depth>
+      </history>
+      <durability>
+        <kind>VOLATILE</kind>
+      </durability>
+    </qos>
+  </data_reader>
+
+  <!-- /visual_servo/cmd_vel: always only the newest Twist -->
+  <data_writer profile_name="cmd_vel_latest">
+    <qos>
+      <reliability>
+        <kind>RELIABLE</kind>
+      </reliability>
+      <history>
+        <kind>KEEP_LAST</kind>
+        <depth>1</depth>
+      </history>
+      <durability>
+        <kind>VOLATILE</kind>
+      </durability>
+    </qos>
+  </data_writer>
+</profiles>