chore(04-01): add Phase 4 deps and create splash module

- Add notify = "6.1", ansi-to-tui = "8.0", walkdir = "2.5" to Cargo.toml
- Create src/splash.rs with load_splash() using IntoText trait
- Add mod splash to main.rs module declarations
- Verified single ratatui-core v0.1.0 in dependency tree

src/main.rs

@@ -3,6 +3,7 @@ mod config;
 mod highlighter;
 mod renderer;
 mod signals;
+mod splash;
 mod terminal;
 mod vault;
 

src/splash.rs

@@ -0,0 +1,25 @@
+//! ANSI art splash screen loader for bbs-md.
+//!
+//! Reads `splash.txt` from the vault root and parses ANSI SGR escape codes
+//! into ratatui `Line` objects via the `ansi-to-tui` crate.
+//!
+//! # Graceful degradation
+//!
+//! If `splash.txt` is missing or cannot be parsed, `load_splash()` returns
+//! `None`. The caller (index.md navigation) renders normally without any
+//! splash header — no error is shown to the user.
+
+use std::path::Path;
+use ansi_to_tui::IntoText;
+use ratatui::text::Line;
+
+/// Load ANSI art from `splash.txt` in the vault root.
+///
+/// Returns `None` if the file doesn't exist or cannot be parsed.
+/// Returns `Some(lines)` where lines are ratatui `Line<'static>` objects
+/// ready to prepend to the index.md content.
+pub fn load_splash(vault_path: &Path) -> Option<Vec<Line<'static>>> {
+    let bytes: Vec<u8> = std::fs::read(vault_path.join("splash.txt")).ok()?;
+    let text = bytes.into_text().ok()?;
+    Some(text.lines)
+}