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, 17 insertions, 0 deletions

diff --git a/src/action.rs b/src/action.rs
new file mode 100644
index 0000000..29ee079
--- /dev/null
+++ b/src/action.rs
@@ -0,0 +1,17 @@
+use serde::{Deserialize, Serialize};
+use strum::Display;
+
+/// Application-level events, distinct from [`crate::buffer::command::Command`],
+/// which is what key bindings name. `Action` is what the event loop routes;
+/// `Command` is what the editor executes.
+#[derive(Debug, Clone, PartialEq, Eq, Display, Serialize, Deserialize)]
+pub enum Action {
+    Tick,
+    Render,
+    Resize(u16, u16),
+    Suspend,
+    Resume,
+    Quit,
+    ClearScreen,
+    Error(String),
+}