fix: add missing clap attribute to no_content_indexing (#754) (#765)

The no_content_indexing field lacked its #[arg(long = ...)] attribute,
so clap treated it as a positional with a SetTrue action. Debug builds
panicked on any invocation; release builds exposed [NO_CONTENT_INDEXING]
as a positional and rejected --no-content-indexing.

Closes #754

Co-authored-by: gustav-fff <286169375+gustav-fff@users.noreply.github.com>

crates/fff-mcp/src/main.rs

@@ -131,6 +131,7 @@ pub(crate) struct Args {
 
     /// Disable the content index built after the initial scan.
     /// This makes grep calls slower but consumes less RAM (recommended to not turn off)
+    #[arg(long = "no-content-indexing")]
     no_content_indexing: bool,
 
     /// Explicitly enable content indexing even when `--no-warmup` is set.