ci(claude): add review-pr skill for domain-aware PR reviews (#26814)

* ci(claude): add review-pr skill for domain-aware PR reviews

Add a Claude Code skill that reviews pull requests with checks
tailored to the domains touched (estimation, control, drivers,
simulation, system, CI/build, messages, board additions).

Built from analysis of 800+ PR reviews across 8 PX4 maintainers.
Includes merge strategy recommendation, interactive dialog for
submitting reviews, and human-sounding PR comment formatting.

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

* ci(copilot): add domain-scoped review instructions for GitHub Copilot

Add .github/instructions/ files that give GitHub Copilot PR reviews
the same domain-aware context as the Claude Code review-pr skill.

Each file is scoped via applyTo to the relevant source paths:
core review, estimation, control, drivers/CAN, simulation, system,
CI/build, messages/protocol, and board additions.

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

* fix(claude): address Copilot review feedback

- Fix step reference in review-pr skill (step 8 -> step 9)
- Capitalize CMake consistently in skill and Copilot instructions

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

---------

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

.github/instructions/messages.instructions.md

@@ -0,0 +1,13 @@
+---
+applyTo: "msg/**,src/modules/mavlink/**,src/modules/uxrce_dds_client/**"
+---
+
+# Messages/Protocol Review Guidelines
+
+In addition to the core code review guidelines:
+
+- Backwards compatibility: will this break QGC, post-flight tools, or uLog parsers?
+- uORB: `timestamp` for publication metadata, `timestamp_sample` close to physical sample, include `device_id`
+- Don't version messages unless strictly needed
+- Parameter UX: will this confuse users in a GCS? Every new param is a configuration burden
+- MAVLink: use library constants, don't implement custom stream rates