feat: make rusty-claude-cli usable end-to-end

Wire the CLI to the Anthropic client, runtime conversation loop, and MVP in-tree tool executor so prompt mode and the default REPL both execute real turns instead of scaffold-only commands.

Constraint: Proxy auth uses ANTHROPIC_AUTH_TOKEN as the primary x-api-key source and may stream extra usage fields
Constraint: Must preserve existing scaffold commands while enabling real prompt and REPL flows
Rejected: Keep prompt mode on the old scaffold path | does not satisfy end-to-end CLI requirement
Rejected: Depend solely on raw SSE message_stop from proxy | proxy/event differences required tolerant parsing plus fallback handling
Confidence: medium
Scope-risk: moderate
Reversibility: clean
Directive: Keep prompt mode tool-free unless the one-shot path is explicitly expanded and reverified against the proxy
Tested: cargo test -p api; cargo test -p tools; cargo test -p runtime; cargo test -p rusty-claude-cli; cargo build; cargo run -p rusty-claude-cli -- prompt "say hello"; printf '/quit\n' | cargo run -p rusty-claude-cli --
Not-tested: Full interactive tool_use roundtrip against the proxy in REPL mode

rust/crates/rusty-claude-cli/src/input.rs

@@ -1,4 +1,4 @@
-use std::io::{self, Write};
+use std::io::{self, IsTerminal, Write};
 
 use crossterm::cursor::MoveToColumn;
 use crossterm::event::{self, Event, KeyCode, KeyEvent, KeyModifiers};
@@ -100,6 +100,10 @@ impl LineEditor {
     }
 
     pub fn read_line(&self) -> io::Result<Option<String>> {
+        if !io::stdin().is_terminal() || !io::stdout().is_terminal() {
+            return self.read_line_fallback();
+        }
+
         enable_raw_mode()?;
         let mut stdout = io::stdout();
         let mut input = InputBuffer::new();
@@ -125,6 +129,23 @@ impl LineEditor {
         }
     }
 
+    fn read_line_fallback(&self) -> io::Result<Option<String>> {
+        let mut stdout = io::stdout();
+        write!(stdout, "{}", self.prompt)?;
+        stdout.flush()?;
+
+        let mut buffer = String::new();
+        let bytes_read = io::stdin().read_line(&mut buffer)?;
+        if bytes_read == 0 {
+            return Ok(None);
+        }
+
+        while matches!(buffer.chars().last(), Some('\n' | '\r')) {
+            buffer.pop();
+        }
+        Ok(Some(buffer))
+    }
+
     fn handle_key(key: KeyEvent, input: &mut InputBuffer) -> EditorAction {
         match key {
             KeyEvent {