feat: implement Helix-style modal buffer under DO-178C DAL-C

The repository was an unmodified ratatui component template: no editor
code, JSON5 config, and placeholder widgets. This establishes the first
working baseline — `moji <file>` opens a file into a ropey rope and edits
it with Helix selection-first semantics.

Requirements, implementation and tests land together because they must:
the traceability check rejects requirements with no implementation and
tests naming requirements that do not exist, so neither half is a valid
commit on its own.

Package renamed to mojibake-editor (mojibake was taken on crates.io);
binary is moji, library target stays mojibake.

Class:        New behaviour
Requirements: MJB-HLR-001..019, MJB-LLR-001..205
Derived:      MJB-DR-001..007 (DR-001 resolved, six open for review)
Verified:     cargo build; clippy --all-targets -D warnings clean;
              cargo test 294 passing; ./scripts/check-trace.sh 98/98/98;
              cargo package clean

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

1 files changed, 37 insertions, 0 deletions

diff --git a/build.rs b/build.rs
new file mode 100644
index 0000000..20c813a
--- /dev/null
+++ b/build.rs
@@ -0,0 +1,37 @@
+use anyhow::Result;
+use vergen_gix::{Build, Cargo, Emitter, Gix};
+
+/// Fallback used when the crate is built outside a git checkout (e.g. from a
+/// packaged `.crate` file), so `env!("VERGEN_GIT_REMOTE_URL")` always resolves.
+const UNKNOWN_REMOTE: &str = "unknown";
+
+fn main() -> Result<()> {
+    let build = Build::all_build();
+    let gix = Gix::all_git();
+    let cargo = Cargo::all_cargo();
+    Emitter::default()
+        .default_on_error()
+        .add_instructions(&build)?
+        .add_instructions(&gix)?
+        .add_instructions(&cargo)?
+        .emit()?;
+
+    emit_git_remote_url();
+    Ok(())
+}
+
+/// vergen only reports the local checkout (sha, branch, describe...), so read the
+/// `origin` remote out of the same repository and expose it alongside the rest of
+/// the `VERGEN_GIT_*` variables.
+fn emit_git_remote_url() {
+    let url = git_remote_url().unwrap_or_else(|| UNKNOWN_REMOTE.to_string());
+    println!("cargo:rustc-env=VERGEN_GIT_REMOTE_URL={url}");
+    println!("cargo:rerun-if-changed=.git/config");
+}
+
+fn git_remote_url() -> Option<String> {
+    let repo = gix::discover(env!("CARGO_MANIFEST_DIR")).ok()?;
+    let remote = repo.find_remote("origin").ok()?;
+    let url = remote.url(gix::remote::Direction::Fetch)?;
+    Some(url.to_bstring().to_string())
+}