docs: remove main.c references, add tools/ directory

main.c no longer exists. Remove run commands from README and
AGENTS.md build sections. Add tools/telemetry.c to source layout
trees in both files.

AGENTS.md

@@ -44,16 +44,6 @@ Run tests and generate coverage HTML:
 ninja -C build-cov coverage
 ```
 
-Run (Linux/macOS):
-```sh
-./build/main /dev/ttyUSB0
-```
-
-Run (Windows):
-```sh
-./build/main.exe COM3
-```
-
 ### Dependencies
 
 Dependencies are managed via custom `Find*.cmake` scripts in `deps/`.
@@ -145,7 +135,8 @@ celrs/
   serial.h / serial.c  Serial port abstraction (Win/POSIX stubs)
   logger.h / logger.c  Level-filtering logger
   log_write.h/.c       stdout log sink
-main.c                 Entry point — demo heartbeat + read
+tools/
+  telemetry.c          Telemetry read tool
 tests/
   test_crsf.c          CRSF CRC, parse, build tests
   test_serial.c        Serial open/close/stub tests

README.md

@@ -70,20 +70,6 @@ mock files are excluded. Requires GCC or Clang with gcov support, and
 > build that includes compiler-rt. A custom Clang without compiler-rt
 > will fail at link time.
 
-## Run
-
-Connect your ELRS TX module via USB, then run:
-
-Windows:
-```sh
-./build/main.exe COM3
-```
-
-Linux / macOS:
-```sh
-./build/main /dev/ttyUSB0
-```
-
 ## Architecture
 
 ```
@@ -92,7 +78,8 @@ celrs/
   serial.h / serial.c  Serial port abstraction (Win/POSIX)
   logger.h / logger.c  Level-filtering logger
   log_write.h/.c       stdout log sink
-main.c                 Entry point — demo heartbeat + read
+tools/
+  telemetry.c          Telemetry read tool
 tests/
   test_crsf.c          CRSF CRC, parse, build tests
   test_serial.c        Serial open/close/stub tests