feat: complete Rust port of claude-statusline

Port the entire 2236-line bash statusline script to Rust.
Implements all 25 sections, 3-phase layout engine (render, priority
drop, flex/justify), file-based caching with flock, 9-level terminal
width detection, trend sparklines, and deep-merge JSON config.

Release binary: 864K with LTO. Render time: <1ms warm.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/lib.rs

@@ -0,0 +1,15 @@
+pub mod error;
+pub use error::Error;
+pub mod cache;
+pub mod color;
+pub mod config;
+pub mod format;
+pub mod glyph;
+pub mod input;
+pub mod layout;
+pub mod metrics;
+pub mod section;
+pub mod shell;
+pub mod theme;
+pub mod trend;
+pub mod width;