bench: every board-runnable tool ported to the bench page

The remaining bench diagnostics run from forgetest's #bench tab. The
tools that also run from a LAN host share scripts/bench/gfbench.py:
GF_HOST names a remote machine (host mode, sysfs through ssh, Grbl and
forgectrl over the LAN); unset, the tool runs on the board itself
(local mode, sysfs directly, everything on 127.0.0.1), which is how the
page runs them - with GF_HOST=127.0.0.1, the panel token in GF_TOKEN
and their data files under <data>/bench/ (FORGETEST_BENCH_DATA). The
helper also reads a machine setting from forgectrl, or from the settings
file on the board while forgectrl is stopped.

Ported: pwm_sweep / pwm_hold (scope = a takeover; the latch relocked,
the write refused if FIRE or LASER_ON reads active), pwm_stream_test
(PASS/FAIL exit), flow_characterize, flow_recheck_char,
flow_warm_validate and flow_matrix (takeovers: forgectrl owns the
thermal hardware, so the page's takeover replaces the tools' own
controller stop/restart, whose command line predated the supervisor;
results and logs in the bench data directory), flow_sustained,
fan_test, temp_calibrate (dry; watch bounded in seconds; the threshold
and the coolant conversion from the shared code), flow_escalate_drill
(cool_confirm_max_s shortened through forgectrl's settings for the
drill and restored; the setting's minimum is the default budget), and
live_fire_drills (<drill> [S] [F], all six drills, host from GF_HOST,
token from the board). flow_matrix joins the registry. What stays
unported cannot run against the machine at all: the two null-sink CI
harnesses and the .puls decoder.

Runner: a scope tool runs inside the takeover wrapper; the bench
environment above is passed to every tool. Tests: test_bench_registry
(registry <-> scripts/bench consistency, every ported tool builds its
command line, every script compiles, gfbench host/local modes) and the
server test (scope tool takeover, the environment reaching the tool).
Local mode smoke-run on the bench (temp_calibrate watch, setting, token)
from /tmp, removed after.

No catalog consequence: bench tools are not image components (dev-only
forgetest); the acceptance catalog is unchanged.

scripts/bench/flow_characterize.py

@@ -10,43 +10,17 @@ climbs. This measures both signatures and prints the separation.
 Phases: baseline (heater off) -> flow (heater on, pump on) -> no-flow
 (pump off) -> recovery (pump on). Restores heater off / pump on.
 
-Run with the controller stopped, or accept that it will fight you: the
-driver only writes the heater on M8/M9 transitions, so an idle driver
-leaves this alone.
+Drives the heater and pump directly, so it runs with forgectrl (the
+thermal-hardware owner) and the controller stopped: the bench page's
+takeover does that; from a host, stop them first. Runs on the board or
+from a host (gfbench: GF_HOST).
+
+Usage: flow_characterize.py [heater_pct]   (default 10)
 """
-import math
-import os
-import shlex
-import subprocess
 import sys
 import time
 
-HOST = os.environ.get('GF_HOST')
-if not HOST:
-    raise SystemExit('set GF_HOST to the machine IP address')
-# ssh client used to reach the board; override for a wrapper, e.g.
-# GF_SSH='wsl -d <distro> -- ssh'.
-SSH = shlex.split(os.environ.get('GF_SSH', 'ssh'))
-
-# Factory B-equation conversion (see kernel-module-glowforge/UAPI.md).
-F = 1024.0 * 1.3
-RD = 10000.0
-BETA = 3380.0
-RINF = 10000.0 * math.exp(-3380.0 / 298.15)
-
-
-def degc(raw):
-    if raw <= 0 or raw >= F:
-        return float('nan')
-    r = RD / (F / raw - 1.0)
-    return BETA / math.log(r / RINF) - 273.15
-
-
-def board(cmd):
-    r = subprocess.run(SSH + ['-o', 'PreferredAuthentications=none',
-                              'root@' + HOST, cmd],
-                       capture_output=True, text=True, timeout=30)
-    return r.stdout.strip()
+from gfbench import board, degc
 
 
 def sample():