Refactor CLI build handling into helper functions (#82)

* Refactor CLI build handling

* Deduplicate Ninja invocation and expand tests

* Remove trailing comma from lint attribute

* Apply mdtablefix to srgn doc

* Expose Ninja constant for reuse

- publish NINJA_PROGRAM so tests can import the default executable\n- point cucumber steps at the constant instead of repeating the string\n- tidy srgn guide paragraph and narrow test helper lint

* Support Ninja override via env var

Author: leynos

AGENTS.md

@@ -150,13 +150,13 @@ project:
   with a backslash.
 - Prefer single line versions of functions where appropriate. I.e.,
 
-  ```
+  ```rust
   pub fn new(id: u64) -> Self { Self(id) }
   ```
 
   Instead of:
 
-  ```
+  ```rust
   pub fn new(id: u64) -> Self {
       Self(id)
   }
@@ -205,12 +205,17 @@ project:
 The following tooling is available in this environment:
 
 - `mbake` – A Makefile validator. Run using `mbake validate Makefile`.
-- `strace` – Traces system calls and signals made by a process; useful for debugging runtime behaviour and syscalls.
-- `gdb` – The GNU Debugger, for inspecting and controlling programs as they execute (or post-mortem via core dumps).
-- `ripgrep` – Fast, recursive text search tool (`grep` alternative) that respects `.gitignore` files.
+- `strace` – Traces system calls and signals made by a process; useful for
+  debugging runtime behaviour and syscalls.
+- `gdb` – The GNU Debugger, for inspecting and controlling programs as they
+  execute (or post-mortem via core dumps).
+- `ripgrep` – Fast, recursive text search tool (`grep` alternative) that
+  respects `.gitignore` files.
 - `ltrace` – Traces calls to dynamic library functions made by a process.
-- `valgrind` – Suite for detecting memory leaks, profiling, and debugging low-level memory errors.
-- `bpftrace` – High-level tracing tool for eBPF, using a custom scripting language for kernel and application tracing.
+- `valgrind` – Suite for detecting memory leaks, profiling, and debugging
+  low-level memory errors.
+- `bpftrace` – High-level tracing tool for eBPF, using a custom scripting
+  language for kernel and application tracing.
 - `lsof` – Lists open files and the processes using them.
 - `htop` – Interactive process viewer (visual upgrade to `top`).
 - `iotop` – Displays and monitors I/O usage by processes.
@@ -219,16 +224,21 @@ The following tooling is available in this environment:
 - `bat` – `cat` clone with syntax highlighting, Git integration, and paging.
 - `delta` – Syntax-highlighted pager for Git and diff output.
 - `tcpdump` – Captures and analyses network traffic at the packet level.
-- `nmap` – Network scanner for host discovery, port scanning, and service identification.
+- `nmap` – Network scanner for host discovery, port scanning, and service
+  identification.
 - `lldb` – LLVM debugger, alternative to `gdb`.
 - `eza` – Modern `ls` replacement with more features and better defaults.
 - `fzf` – Interactive fuzzy finder for selecting files, commands, etc.
 - `hyperfine` – Command-line benchmarking tool with statistical output.
 - `shellcheck` – Linter for shell scripts, identifying errors and bad practices.
 - `fd` – Fast, user-friendly `find` alternative with sensible defaults.
-- `checkmake` – Linter for `Makefile`s, ensuring they follow best practices and conventions.
-- `srgn` – [Structural grep](https://github.com/alexpovel/srgn), searches code and enables editing by syntax tree patterns (see `docs/srgn.md` for a complete guide).
-- `difft` **(Difftastic)** – Semantic diff tool that compares code structure rather than just text differences.
+- `checkmake` – Linter for `Makefile`s, ensuring they follow best practices and
+  conventions.
+- `srgn` – [Structural grep](https://github.com/alexpovel/srgn), searches code
+  and enables editing by syntax tree patterns (see `docs/srgn.md` for a
+  complete guide).
+- `difft` **(Difftastic)** – Semantic diff tool that compares code structure
+  rather than just text differences.
 
 ## Key Takeaway