fix(tui): allow free scrolling during progressive loading

total_lines() was returning sampled_line_count() (only ~300 lines from the initial 64KB scan) during the Loading state, capping the scroll range. Use estimated_lines instead so the user can scroll to any position while indexing runs in the background. get_line() already supports incremental forward scanning on demand.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

crates/tui/src/app.rs

@@ -634,8 +634,16 @@ impl App {
     pub fn total_lines(&self) -> usize {
         match &self.loading_state {
             AppLoadingState::Ready { reader } => reader.line_count(),
-            AppLoadingState::Loading { reader, .. } => {
-                reader.sampled_line_count()
+            AppLoadingState::Loading {
+                reader,
+                estimated_lines,
+                ..
+            } => {
+                // Use estimated total lines (not sampled_line_count) so the user can
+                // scroll freely during indexing.  get_line() incrementally scans
+                // forward on demand, so lines beyond the initial 64KB are still
+                // accessible.  The .max() guards against under-estimates.
+                (*estimated_lines as usize).max(reader.sampled_line_count())
             }
             _ => 0,
         }