Initial commit: DPM core library, CLI, bundled info module, and tests

docs/BUILD.md

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+# Building DPM Core
+
+## Prerequisites
+
+- GCC/G++ supporting C++20
+- CMake 3.22 or later
+- Make
+- Doxygen (optional, for the code reference)
+- pdflatex and makeindex (optional, for the PDF code reference)
+
+The library itself depends only on libc, libstdc++, and libdl, so it builds and runs on a minimal system.
+
+## Building for development
+
+```
+cmake -B <build-dir> -DCMAKE_BUILD_TYPE=Debug
+cmake --build <build-dir>
+```
+
+Artifacts land in:
+
+```
+<build-dir>/bin/dpm             the CLI
+<build-dir>/lib/libdpm-core.so  the core library
+<build-dir>/modules/info.so     the bundled info module
+```
+
+The dpm binary built here finds the locally built libdpm-core.so on its own — an embedded library search path points it at the lib/ directory next to it in the build tree, so running it directly uses the core you just built with nothing to set up first. This is only the default: LD_LIBRARY_PATH takes precedence over the embedded path, so the binary can be pointed at any other core, including the system-installed one.
+
+### Running the tests
+
+```
+ctest --test-dir <build-dir> --output-on-failure
+```
+
+This runs the core API test binary (which exercises the full load-time validation matrix against the fixture modules in tests/fixtures/) and the CLI end-to-end tests.
+
+### Running the CLI from the build tree
+
+The build tree plus the test fixtures form a complete self-contained environment; no installation is required. Point the CLI at local paths with its override flags:
+
+```
+<build-dir>/bin/dpm --config-dir ./tests/fixtures/conf --module-path <build-dir>/modules info version
+```
+
+The flags --config-dir, --module-path, --root, and --log-level each redirect the corresponding system default; --root sets the target root that package-operation modules act on.
+
+## Generating the code reference
+
+When Doxygen is present, the build offers a docs target that generates the API and source reference from the documentation comments carried in the headers and sources. Two output formats are available as configure-time options:
+
+- **-DDPM_DOCS_PDF** (default ON) — PDF reference, via Doxygen's native LaTeX output; requires pdflatex and makeindex
+- **-DDPM_DOCS_HTML** (default OFF) — HTML reference
+
+Generate and compile the PDF reference:
+
+```
+cmake --build <build-dir> --target docs-pdf
+```
+
+The PDF lands at <build-dir>/docs/latex/refman.pdf.
+
+With DPM_DOCS_HTML enabled at configure time, the docs target additionally produces the HTML reference in <build-dir>/docs/html:
+
+```
+cmake -B <build-dir> -DDPM_DOCS_HTML=ON
+cmake --build <build-dir> --target docs
+```
+
+## Building, testing, and installing a release
+
+One build tree carries the whole sequence — the test suite builds and runs in any configuration, so the artifacts that get tested are the artifacts that get installed:
+
+```
+cmake -B <build-dir> -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr
+cmake --build <build-dir>
+ctest --test-dir <build-dir> --output-on-failure
+cmake --install <build-dir>
+```
+
+This is the packaging flow: configure once, build once, test what was built, install what was tested. Omit -DCMAKE_INSTALL_PREFIX=/usr for a /usr/local install. Under the install prefix this installs:
+
+```
+bin/dpm                   the CLI
+lib/libdpm-core.so        the core library
+lib/dpm/modules/info.so   the bundled info module
+include/dpm/              the public header
+```
+
+Core configuration installs to /etc/dpm/conf.d/core.conf regardless of prefix.
+
+