Add git sources, check-updates, repos submodule, improve docs

dpack features:
- Git source support: packages can specify [source].git for cloning
  instead of tarball download. Supports branch, tag, and commit pinning.
  SHA256 can be set to "SKIP" for git sources.
- check-updates command: queries upstream APIs (GitHub releases/tags)
  to find available updates. Packages set [source].update_check URL.
- CheckUpdates CLI subcommand wired into main.rs

Package changes:
- FreeCAD updated to weekly-2026.03.19 development builds
- dwl: added update_check URL and git source documentation
- src/repos extracted to standalone git repo (danny8632/repos.git)
  and added as git submodule

Documentation:
- All 7 README.md files updated with detailed requirements sections
  including which Linux distros are supported, exact package names
  for Arch/Ubuntu/Fedora, and clear notes about which components
  require Linux vs can be built on macOS
- dpack README: added git source and check-updates documentation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/dpack/README.md

@@ -16,12 +16,47 @@ A source-based package manager for DarkForge Linux, positioned between CRUX's `p
 
 ## Requirements
 
-- Rust 1.75+ (build)
-- Linux (runtime — uses Linux namespaces for sandboxing)
-- bubblewrap (`bwrap`) for sandboxed builds (optional, falls back to direct execution)
-- `curl` or `wget` for source downloads
-- `tar` for source extraction
-- `readelf` or `objdump` for shared library scanning
+**Build-time (compiling dpack itself):**
+
+dpack is written in Rust and can be built on any platform with a Rust toolchain:
+
+- Rust 1.75+ with Cargo (install via https://rustup.rs)
+- A C linker (gcc or clang) — needed by some Rust dependencies
+- Works on Linux and macOS for development, but runtime features require Linux
+
+```bash
+# macOS (Homebrew)
+brew install rustup && rustup-init
+
+# Arch Linux
+sudo pacman -S rust
+
+# Ubuntu / Debian
+curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
+```
+
+**Runtime (using dpack to build/install packages):**
+
+dpack must run on a Linux system (it uses Linux-specific features):
+
+- Linux kernel 5.4+ (for namespace support)
+- `bash` (build scripts are bash)
+- `curl` or `wget` (source tarball downloads)
+- `git` (for git-source packages)
+- `tar` (source extraction)
+- `readelf` or `objdump` (shared library scanning — part of binutils)
+- bubblewrap (`bwrap`) for sandboxed builds (optional — falls back to direct execution)
+- A C/C++ compiler (gcc or clang) and make (for building packages)
+
+On the DarkForge system itself, all runtime dependencies are provided by the base system. On another Linux distro for testing:
+
+```bash
+# Arch Linux
+sudo pacman -S base-devel bubblewrap curl git
+
+# Ubuntu / Debian
+sudo apt install build-essential bubblewrap curl git binutils
+```
 
 ## Building
 
@@ -33,7 +68,11 @@ cargo build --release
 The binary is at `target/release/dpack`. Install it:
 
 ```bash
+# On Linux
 sudo install -m755 target/release/dpack /usr/local/bin/
+
+# For development/testing (from the repo root)
+cargo run --release -- install zlib
 ```
 
 ## Usage
@@ -64,6 +103,9 @@ dpack list
 # Check for file conflicts and shared library issues
 dpack check
 
+# Check for available updates (compares installed vs repo + upstream)
+dpack check-updates
+
 # Convert foreign package formats
 dpack convert /path/to/Pkgfile                          # CRUX → dpack TOML (stdout)
 dpack convert /path/to/curl-8.19.0.ebuild -o curl.toml  # Gentoo → dpack TOML (file)
@@ -158,6 +200,42 @@ ldflags = ""
 
 The `system` field is a hint: `autotools`, `cmake`, `meson`, `cargo`, or `custom`.
 
+### Git sources
+
+Instead of downloading a tarball, dpack can clone a git repository directly. This is useful for building from the latest development branch or a specific commit:
+
+```toml
+[source]
+url = ""                                         # can be empty for git sources
+sha256 = "SKIP"                                  # integrity verified by git
+git = "https://github.com/FreeCAD/FreeCAD.git"   # clone URL
+branch = "main"                                  # checkout this branch
+
+# Or pin to a tag (supports ${version} expansion):
+# tag = "v${version}"
+
+# Or pin to a specific commit:
+# commit = "abc123def456"
+```
+
+When `git` is set, dpack clones the repository (with `--depth 1` for branches/tags) into the build directory. The `branch`, `tag`, and `commit` fields control what gets checked out (in priority order: commit > tag > branch > default).
+
+### Upstream update checking
+
+Packages can specify an `update_check` URL in the `[source]` section. When you run `dpack check-updates`, it queries these URLs and compares the result against your installed version.
+
+```toml
+[source]
+url = "https://example.com/foo-${version}.tar.xz"
+sha256 = "..."
+update_check = "https://api.github.com/repos/owner/repo/releases/latest"
+```
+
+Supported URL patterns:
+- **GitHub releases API** — parses `tag_name` from the JSON response
+- **GitHub/Gitea tags API** — parses the first tag name
+- **Plain URL** — the response body is treated as the version string
+
 ## Running Tests
 
 ```bash