fix(cmake): require cpp-httplib >= 0.14 in pkg-config check

[bburda]

Pull Request

Summary

Add minimum version constraint (>=0.14) to pkg_check_modules() in medkit_find_cpp_httplib() so that old system packages (e.g. 0.10.x on Ubuntu 22.04 Jammy) are rejected and the cmake/source-build fallback path is used instead.

Also improves error reporting with a clear FATAL_ERROR message when no suitable cpp-httplib is found, and updates installation docs with prerequisites and troubleshooting guidance.

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Issue

• closes [BUG] Build fails on Humble when system libcpp-httplib-dev is installed - old cpp-httplib version lacks StatusCode and std::string overloads #225

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Type

• Bug fix
• New feature or tests
• Breaking change
• Documentation only

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Testing

• On Jazzy/Noble: no behavior change - pkg-config finds the system package (0.18.x) which satisfies >=0.14
• On Humble/Jammy with libcpp-httplib-dev installed: pkg-config now rejects 0.10.x, falls through to cmake config path (source-built cpp-httplib)
• On Humble/Jammy without any cpp-httplib: clear FATAL_ERROR with installation instructions instead of a cryptic find_package(httplib REQUIRED) failure

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Checklist

• Breaking changes are clearly described (and announced in docs / changelog if needed)
• Tests were added or updated if needed
• Docs were updated if behavior or public API changed

[Copilot]

Pull request overview

This pull request fixes a build failure on ROS 2 Humble (Ubuntu 22.04) when the system libcpp-httplib-dev package is installed. The system package provides cpp-httplib 0.10.x, which lacks the httplib::StatusCode enum and std::string API overloads that ros2_medkit requires (available in cpp-httplib >= 0.14). The fix adds a minimum version constraint to the pkg-config check so that old versions are rejected and the CMake/source-build fallback path is used instead. It also improves error reporting with clear installation instructions.

Changes:

• Add >=0.14 version constraint to pkg_check_modules() in the cpp-httplib finder macro
• Convert find_package(httplib REQUIRED) to QUIET mode with explicit error handling and helpful FATAL_ERROR message containing installation instructions
• Update installation documentation to explain the version requirement and provide clear removal/installation steps for Humble users
• Add troubleshooting section for the specific httplib::StatusCode has not been declared error

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
cmake/ROS2MedkitCompat.cmake	Adds version constraint to pkg-config check, converts to QUIET mode with explicit error handling, improves status messages
docs/installation.rst	Updates prerequisites note and adds troubleshooting section with clear installation instructions for cpp-httplib >= 0.14