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_sustained.py

@@ -6,38 +6,20 @@ job, and does the loop reach equilibrium or climb without bound? Runs
 the driver's real check cadence (M8 held for the duration) with the
 cut-profile fans, logging bulk coolant temperature and every verdict.
 
+Needs the controller running with forgectrl's cooling engine (the
+verdict lines arrive on the Grbl socket). Runs on the board or from a
+host (gfbench: GF_HOST).
+
 Usage: flow_sustained.py [minutes]   (default 30)
 """
-import math
-import os
-import shlex
 import re
 import socket
-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'))
-F = 1024.0 * 1.3
-RD, BETA = 10000.0, 3380.0
-RINF = 10000.0 * math.exp(-3380.0 / 298.15)
+from gfbench import HOST, board, degc, setting
 
-
-def degc(raw):
-    r = RD / (F / float(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()
+THRESHOLD = float(setting('cool_flow_rise', 14.4))    # forgectrl's configured threshold
 
 
 def temps():
@@ -92,8 +74,8 @@ print()
 print('checks run: %d over %.0f min' % (len(verdicts), minutes))
 if verdicts:
     rises = [v[1] for v in verdicts]
-    print('rise values: min=%.2f max=%.2f mean=%.2f  (threshold 13.7)'
-          % (min(rises), max(rises), sum(rises) / len(rises)))
+    print('rise values: min=%.2f max=%.2f mean=%.2f  (threshold %.1f)'
+          % (min(rises), max(rises), sum(rises) / len(rises), THRESHOLD))
     print('false faults: %d' % sum(1 for v in verdicts if v[2]))
 print('loop temperature: start %.2f -> end %.2f (%+.2f C), peak %.2f'
       % (u0, u, u - u0, peak_up))