[biobo-bot]

Summary

Rewrite README.md so it reflects the v0.9.5 API and the build/packaging
setup that actually exists, and fix the requirements listed in
docs/index.md.

Changes

• README hero: a short std::variant<int, std::string> match that shows a
  literal case, bindings whose values the handlers use, guards that pick
  the branch, and the _ fallback.
• README Quick Tour restructured: literals and value guards, structs,
  structured-binding placeholders, std::variant (is<T> / alt<I>),
  combinators, an event-dispatch example, and cached case packs.
• New Core Concepts table summarizing the public API.
• New Requirements section taken from cmake/CheckCompilerVersion.cmake
  (GCC 11, Clang 12, AppleClang 14, MSVC 19.30, clang-cl 18) plus the
  compilers and standards covered by CI.
• Installation: vcpkg, FetchContent (v0.9.5), install + find_package,
  and subdirectory / include-path options.
• Building the Tests lists the PTN_* CMake options; adds a License
  section and links to AGENTS.md and SECURITY.md.
• docs/index.md: correct the MSVC minimum (19.30 / VS2022, not 2019),
  list the CMake-checked minimums, and drop the macOS claim (AppleClang 14
  is accepted by the CMake check but not tested in CI).

Testing

• Compiled every C++ snippet in the new README with Clang in C++17 and
  C++20 using -Wall -Wextra -Werror, with asserts on the results; all
  passed.
• Built and ran ptn_tests locally on this branch's base: all tests
  passed (the separate C++20 member-names target was not built).

[biobo-bot]

Reviewed the README rewrite and the docs/index.md requirements fix. This looks good to me, and I have no blocking issues.

What I checked:

• The Requirements tables match cmake/CheckCompilerVersion.cmake (GCC 11, Clang 12, AppleClang 14, MSVC 19.30, clang-cl 18 with an MSVC 19.30+ toolset). Correcting MSVC from "2019" to 19.30 / VS2022 is the right fix.
• The PTN_* options listed under Building the Tests match CMakeLists.txt, and the "on by default only when top-level" note matches PTN_MASTER_PROJECT.
• The FetchContent tag is v0.9.5, and the install + find_package flow turns off tests, benchmarks, and samples, which is sensible for an install-only build.
• The hero and Quick Tour examples use bindings whose values are actually consumed by the handlers, and the guards pick branches as intended. The note that >> binds tighter than || / && is correct C++ precedence.
• The PTN_ON scoping note keeps the important caveat from the old README (captureless lambda, so use namespace scope, C++20 static, or PTN_BIND in C++17) in a shorter form.
• CI on this head is green apart from a couple of jobs still running.

Two optional nits:

• The Performance Tuning link goes to GitHub while the other docs links go to patternia.tech. That's fine, since guide/performance-tuning.md isn't in the mkdocs.yml nav yet. If it gets added later, this link could switch over.
• PTN_DEV_INDEX isn't in the options list. That seems intentional, since it's an IDE-only target.

I'm leaving this as a comment rather than an approval because GitHub doesn't let a PR's author (Biobo Bot) approve its own pull request, so a maintainer needs to approve it.