Fix DMR decoder signal activity and parsing for dsd-fme compatibility

The DSD stderr parser had regex ordering bugs that swallowed voice and
call events as bare slot events, and only matched classic dsd output
format (not dsd-fme). Unmatched lines were silently dropped, leaving
the signal activity panel with nothing to display.

- Reorder regex checks: TG/Src before voice before slot
- Support dsd-fme comma-separated format (TG: x, Src: y)
- Make bare slot regex strict (only standalone "Slot N" lines)
- Forward unmatched DSD lines as raw events for diagnostics
- Add LISTENING state to signal activity panel for raw output
- Show raw decoder output text below synthesizer canvas
- Fix test mocks for find_dsd() tuple return value

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

templates/index.html

@@ -1623,6 +1623,7 @@
                             <span id="dmrSynthStatus" style="color: var(--text-muted); font-size: 9px; font-family: var(--font-mono);">IDLE</span>
                         </div>
                         <canvas id="dmrSynthCanvas" style="width: 100%; height: 70px; background: rgba(0,0,0,0.4); border-radius: 4px; display: block;"></canvas>
+                        <div id="dmrRawOutput" style="font-size: 9px; font-family: var(--font-mono); color: var(--text-muted); margin-top: 4px; height: 14px; overflow: hidden; text-overflow: ellipsis; white-space: nowrap;"></div>
                     </div>
                     <div style="display: grid; grid-template-columns: 1fr 1fr; gap: 12px;">
                         <!-- Call History Panel -->