Move the rtt, etm-trace, target-debug and esp-target-debug skills out to agentrc (#3925)

The four debug skills are generic technique and now install from agentrc,
following #3920; only their "In TinyUSB" examples name this repo. Kept here:
tools/rtt.py as a byte-identical copy of agentrc's script, since hil_util
imports its console classes, with test_hil_rtt.py shrunk to the harness
contract; `tools/build_utils.py board-info <board>`, which prints a board's
JLINK_DEVICE and reference Ozone project for the etm-trace capture script and
refuses conditional or unresolvable definitions. The full rtt move is written
up in the HIL-farm handoff.

Folds #3871 into rtt.py: Windows process-group lifecycle, RTT_JLINK_EXE and
RTT_OPENOCD_EXE overrides, --stop-file cancellation, plus two fixes on top:
arguments are validated before an existing stop file is honored, and SIGINT
and SIGBREAK go through the same orderly teardown as SIGTERM. Regression on
ea4088_quickstart over J-Link; Windows unverified.

CLAUDE.md and the agents say once what comes from agentrc, hand the PR loop
to chief, and wait for Copilot on every push instead of a Claude review.