feat: add AGENTS.md for quick start and CI guidelines; update documentation for dcr add and dcr build commands

docs/commands/dcr-add.md

@@ -5,11 +5,15 @@ Add a dependency to `dcr.toml`.
 ## Usage
 
 ```bash
-dcr add <name> <source> [options]
+dcr add <name> [source] [options]
 ```
 
+If `<source>` is omitted and a registry is configured, DCR will look up the
+package by name in the registry and add it as a version dependency.
+
 ## Sources
 
+- *omitted*: Look up in the configured registry.
 - `path:./path/to/lib`: Local directory.
 - `github:user/repo`: GitHub repository.
 - `gitlab:user/repo`: GitLab repository.
@@ -29,4 +33,5 @@ dcr add my_lib path:./libs/my_lib
 dcr add cool_lib github:user/cool_lib
 dcr add shared_lib gitlab:org/shared --branch develop
 dcr add custom_lib git:git.internal.com/r/lib --tag v1.0.0
+dcr add mylib                    # Looks up in registry
 ```

docs/commands/dcr-build.md

@@ -35,6 +35,7 @@ dcr build --debug --clean
 - `build.platform`
 - `build.cflags`
 - `build.ldflags`
+- `build.ldscript`
 - `build.debug` / `build.release`
 - `build.exclude`
 - `build.include`
@@ -58,6 +59,7 @@ dcr build --debug --clean
 - Profile flag (`--debug` / `--release`) can appear in any argument position (duplicates are rejected).
 - Unknown profile flags return an error.
 - `--target <triple>` builds for specified target (short names: `linux`, `macos`, `windows`).
+- `--verbose` prints the compiler/linker command lines to stderr (also works via `DCR_DEBUG` env var).
 - If no `--target`, builds for `build.targets` or native.
 - Incremental rebuild checks source/object mtime and tracked header dependencies.
 - `--force` skips build cache checks and recompiles.