[M8] reusable libraries: install layout + cargoxx-path deps

CHANGELOG.md

@@ -435,3 +435,66 @@ All notable changes to cargoxx will be documented in this file.
   Added `inputs.bundlers.url = "github:NixOS/bundlers"` (with
   `inputs.nixpkgs.follows = "nixpkgs"`) to keep the closure aligned
   with the project's pinned nixpkgs.
+- M8 multiple binary build artifacts (Cargo `src/bin/` parity).
+  Codegen now routes every executable (`add_executable`) to
+  `${CMAKE_BINARY_DIR}/bin` via `set_target_properties(... RUNTIME_OUTPUT_DIRECTORY ...)`.
+  `buildCppPackage` and `cargoxx run --bin <name>` follow suit, and
+  layout discovery picks up Cargo's `src/bin/<sub>/main.cpp` form
+  (subdir name becomes the binary name). End-to-end fixture
+  `tests/e2e/buildCppPackage/src/bin/extra.cpp` proves a second
+  binary lands in `$out/bin/` alongside the primary.
+- M8 reusable library install layout. `cargoxx`-built libraries now
+  ship a CMake-idiomatic `$out` tree: `lib/lib<name>.a`,
+  `lib/cmake/<name>/{<name>Config.cmake,<name>ConfigVersion.cmake,
+  <name>Targets.cmake}`, `lib/pkgconfig/<name>.pc`, and modules
+  under `include/<name>/` (via `install(TARGETS ... FILE_SET CXX_MODULES ...)`).
+  Codegen emits the install rules + a `Config.cmake.in` template
+  (inline `file(WRITE …)`) consumed by
+  `configure_package_config_file` and `write_basic_package_version_file`,
+  plus a basic `.pc.in` template. The exported library target
+  carries `target_compile_features(... PUBLIC cxx_std_<NN>)` so
+  consumers `find_package`-ing it get the right standard for
+  module BMI regeneration.
+  `buildCppPackage.installPhase` switched from `cp -a build/release/bin/.`
+  to `cmake --install build/release --prefix $out` — bins, libs,
+  headers, config, and pc files all land via one invocation.
+  `project(... VERSION <pkg.version> ...)` is now part of the
+  generated header so `<name>ConfigVersion.cmake` reflects the
+  manifest's version.
+- M8 cargoxx-path dependencies (Cargo's `{ path = "..." }`). The
+  manifest gains a discriminated dep table form:
+  ```toml
+  [dependencies]
+  greeter = { path = "./greeter" }
+  ```
+  `manifest::Dependency` carries `DepSource source` +
+  `optional<string> path`. The parser branches on `path`; unknown
+  dep-table keys still rejected for tables that have neither
+  `version` nor `path`. Round-tripped by the writer.
+  Lockfile schema adds per-package `source_kind` + `source_path`
+  so the consumer's `Cargoxx.lock` records "this dep is built from
+  a cargoxx source tree at `./greeter`" (not nixpkgs).
+  `cmd_build::resolve_path_dep` reads `<path>/Cargoxx.toml` to
+  verify the dep's name matches, then synthesizes a Recipe
+  (`find_package = "<name> CONFIG REQUIRED"`,
+  `targets = ["<name>::<name>"]`, `source = "cargoxx-path"`).
+  Codegen needs no special case — the synthesized recipe flows
+  through the existing `find_package` emission path.
+  `buildCppPackage`'s recursion: `evalDep` branches on
+  `source_kind == "cargoxx-path"` and recurses with
+  `src = src + "/" + source_path`. The resulting derivation joins
+  `buildInputs`; CMake's `CMAKE_PREFIX_PATH` picks it up so the
+  consumer's `find_package(<dep> CONFIG REQUIRED)` resolves
+  against the producer's installed Config.cmake. Path deps must be
+  subdirectories of the consumer's source tree (no sibling form in
+  v1 — sibling deps will land with git/registry sources in 1c/1d).
+  New e2e fixture `tests/e2e/pathDep/`: a `consumer` project with
+  `[dependencies] greeter = { path = "./greeter" }`. `run.sh`
+  generates locks in both, then `nix build .#default` produces a
+  binary that prints "Hello from greeter, world!".
+- M8 design doc at `docs/library-reuse-and-publish.md` covers the
+  full two-part roadmap: library reuse (path → git → registry deps)
+  and Gitea-hosted public registry with `cargoxx publish` + bot
+  validation + binary-cache substitution. Phase 1a (install rules)
+  and Phase 1b (path deps) shipped in this commit; phases 1c, 1d,
+  and 2 remain to be built.