fix: separate logger from dashboard output

Logger writes to stderr so it doesn't corrupt the dashboard on stdout.
Dashboard tracks its own line count and uses cursor-up instead of home
so log messages appear cleanly before/after instead of interleaved.

GOAL.md

@@ -1,7 +0,0 @@
-Implement all TODOs in the codebase.
-
-write test first follow @AGENTS.md, commit when implemented one at a time and it passes.
-
-git push when implemented.
-
-You need to able to run telemetry on COM14 and start receiving data from TX module.

celrs/log_write.c

@@ -2,5 +2,5 @@
 #include <stdio.h>
 
 void cel_log_write(char const* msg) {
-    printf("%s\n", msg);
+    fprintf(stderr, "%s\n", msg);
 }

tools/telemetry.c

@@ -57,7 +57,7 @@ static void sleep_ms(int ms) {
 }
 
 /* --------------------------------------------------------------------------- */
-/* ANSI helpers                                                                */
+/* ANSI helpers — all go to stdout so dashboard owns it                        */
 /* --------------------------------------------------------------------------- */
 
 static void ansi_reset(void) { printf("\033[0m"); }
@@ -67,7 +67,12 @@ static void ansi_yellow(void) { printf("\033[33m"); }
 static void ansi_bold(void) { printf("\033[1m"); }
 static void ansi_dim(void) { printf("\033[2m"); }
 static void ansi_clear_line(void) { printf("\033[2K"); }
-static void ansi_home(void) { printf("\033[H"); }
+
+static void ansi_cursor_up(int n) {
+    char buf[16];
+    snprintf(buf, sizeof(buf), "\033[%dA", n);
+    printf("%s", buf);
+}
 
 /* --------------------------------------------------------------------------- */
 /* Status helpers                                                              */
@@ -223,17 +228,21 @@ static void rssi_color(double dbm) {
 }
 
 /* --------------------------------------------------------------------------- */
-/* Dashboard render                                                            */
+/* Dashboard render — tracks line count for in-place redraw                    */
 /* --------------------------------------------------------------------------- */
 
 static void render_dashboard(dashboard_t const* d,
                               char const* port, int baud,
-                              double elapsed) {
+                              double elapsed, int* lines) {
     double now = (double)time(NULL);
     status_t status = compute_status(now, d->link_t, d->fc_t);
 
-    ansi_home();
-    ansi_clear_line();
+    /* Return to top of dashboard if already drawn */
+    if (*lines > 0) {
+        ansi_cursor_up(*lines);
+    }
+
+    int n = 0;
 
     /* Title */
     ansi_bold();
@@ -241,10 +250,12 @@ static void render_dashboard(dashboard_t const* d,
     ansi_reset();
     printf("  %s @ %d baud  up %.0fs\n",
            port, baud, elapsed);
+    n++;
 
-    /* Status line */
+    /* Status */
     print_status_label(status);
     printf("\n");
+    n++;
 
     /* LINK */
     ansi_bold(); printf("  LINK  "); ansi_reset();
@@ -267,6 +278,7 @@ static void render_dashboard(dashboard_t const* d,
         ansi_dim(); printf("waiting..."); ansi_reset();
     }
     printf("\n");
+    n++;
 
     /* BATT */
     ansi_bold(); printf("  BATT  "); ansi_reset();
@@ -280,6 +292,7 @@ static void render_dashboard(dashboard_t const* d,
         ansi_dim(); printf("waiting..."); ansi_reset();
     }
     printf("\n");
+    n++;
 
     /* IMU */
     ansi_bold(); printf("  IMU   "); ansi_reset();
@@ -293,6 +306,7 @@ static void render_dashboard(dashboard_t const* d,
         ansi_dim(); printf("waiting..."); ansi_reset();
     }
     printf("\n");
+    n++;
 
     /* MODE */
     ansi_bold(); printf("  MODE  "); ansi_reset();
@@ -303,13 +317,16 @@ static void render_dashboard(dashboard_t const* d,
         ansi_dim(); printf("waiting..."); ansi_reset();
     }
     printf("\n");
+    n++;
 
     /* Footer */
     ansi_dim();
     printf("  rx=%d  ignored=%d", d->rx_frames, d->unknown);
     ansi_reset();
     printf("\n");
+    n++;
 
+    *lines = n;
     fflush(stdout);
 }
 
@@ -401,7 +418,7 @@ int main(int argc, char const* argv[]) {
 
     /* Verify module responds to CRSF ping */
     if (verify_connection(port) != 0) {
-        cel_log_warn("Continuing anyway - telemetry may not arrive");
+        cel_log_warn("Continuing anyway — telemetry may not arrive");
     }
 
     /* Create CRSF stream for incremental parsing */
@@ -425,6 +442,7 @@ int main(int argc, char const* argv[]) {
     uint8_t read_buf[256];
     time_t t_start = time(NULL);
     int rc_count = 0;
+    int d_lines = 0; /* dashboard line count for cursor tracking */
 
     while (s_running) {
         /* Read available data */
@@ -454,12 +472,16 @@ int main(int argc, char const* argv[]) {
         /* Redraw dashboard every 100 ms */
         if (rc_count % 5 == 0) {
             double elapsed = difftime(time(NULL), t_start);
-            render_dashboard(&dash, port_path, actual_baud, elapsed);
+            render_dashboard(&dash, port_path, actual_baud, elapsed, &d_lines);
         }
 
         sleep_ms(20);
     }
 
+    /* Move cursor past dashboard before shutdown message */
+    if (d_lines > 0) {
+        printf("\n");
+    }
     cel_log_info("Shutting down...");
     cel_crsf_stream_destroy(stream);
     cel_serial_close(port);