feat: document gyroUnfilt debug fallback in report metadata

When gyroUnfilt data comes from debug[0-2] channels instead of dedicated
gyroUnfilt columns, add a ⚠ note in Metadata with the debug mode name
(e.g. GYRO_SCALED, RC_SMOOTHING). Pilots need to know that unfiltered gyro
spectrums and filtering delay calculations in that report are derived from
debug channels, not actual gyroUnfilt — affecting their interpretation.

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

Author: nerdCopter

src/main.rs

@@ -1697,6 +1697,8 @@ INFO ({input_file_str}): Skipping Step Response input data filtering: {reason}."
         filter_config,
         dynamic_notch,
         rpm_filter,
+        debug_fallback: using_debug_fallback,
+        debug_mode_name: debug_mode_label,
     };
     match report::generate_markdown_report(&flight_report, report_path) {
         Ok(()) => println!("  [OK] Report written."),

src/report.rs

@@ -58,6 +58,9 @@ pub struct FlightReport {
     pub filter_config: Option<AllFilterConfigs>,
     pub dynamic_notch: Option<DynamicNotchConfig>,
     pub rpm_filter: Option<RpmFilterConfig>,
+    /// True when gyroUnfilt came from debug channels instead of dedicated gyroUnfilt columns.
+    pub debug_fallback: bool,
+    pub debug_mode_name: Option<&'static str>,
 }
 
 /// Generate a structured markdown report and write it to `output_path`.
@@ -93,6 +96,16 @@ pub fn generate_markdown_report(
             writeln!(md, "- **{}:** {}", k, v)?;
         }
     }
+    if report.debug_fallback {
+        let mode_str = report
+            .debug_mode_name
+            .map_or(String::new(), |m| format!(" ({})", m));
+        writeln!(
+            md,
+            "- **⚠ gyroUnfilt source:** debug[0-2] fallback{} — unfiltered gyro spectrum and filtering delay derived from debug channels, not dedicated gyroUnfilt columns",
+            mode_str
+        )?;
+    }
     writeln!(md)?;
 
     // --- Filter Configuration ---