Bengle integrated scale calibration wizard

[ChampionDesigns]

Stacked — review the LAST commit only: 7a8f2d4 "Bengle integrated scale calibration wizard".

This lane needs the tare write from the integrated-scale PR and the calibration-flow
navigation from the machine-autonomy PR. A branch cannot root on two unmerged branches,
so it is a merge of both, and GitHub's merge-base falls back to ben/detect-protocol.
The PR therefore lists five commits and ~1,269 lines; only the last commit (882 lines) is
new here. The other four are under review as PRs #1, #2 and #4.

Filed inside the fork so the other PRs' diffs stay clean. It will be re-filed against
decentespresso/de1app once its bases have merged there.

ben/machine-autonomy. Retarget to main once both have merged. 882 insertions, 10 files.

Summary

The Bengle scale uses two load cells and needs a per-cell calibration. This adds a
seven-step wizard driving the firmware's calibration state machine over MMR, and the
calibrate4 page that presents it.

register	access	address	encoding
ScaleCalCmd	W	0x00803880	0 abort, 1 zero, 2 latch
ScaleCalState	R	0x00803884	packed U32
ScaleCalWeight	RW	0x00803888	grams ×10

bits 31:24  Step             0 idle, 1 zeroing, 2 latching, 4 taring, 5 complete, 6 error
bits 23:20  DetectedCell     0 none, 1 cell A, 2 cell B
bits 19:16  SubState         0 settling, 1 averaging, 2 done, 3 error
bits 15:8   SecondsRemaining
bits  7:0   Status           0 ok … 8 not isolated, 255 none

There is no step 3. The set is 0, 1, 2, 4, 5, 6.

Addresses, packing, command values and every enum match decentespresso/decaid, which is
the only other implementation of this word — the two reaprime skins reach the flow through
decaid's REST API rather than decoding it themselves.

The seven steps

Remove platform, zero cells, calibrate first cell, calibrate second cell, replace platform,
tare, verify.

Steps 3 and 4 do not ask which cell is which: the firmware reports DetectedCell from
where the weight was placed, so the user puts it on one side and then the other in either
order.

Changes

scale_calibration.tcl — new file. The ::scale_cal namespace: step state, firmware
state from the last poll, a one-second poll timer that runs only while a measurement is
active, status and progress bound to the page, and validation of the reference mass.

pkgIndex.tcl, gui.tcl, de1_comms.tcl — package registration and requires.

de1_comms.tcl and bluetooth.tcl — decode ScaleCalState and ScaleCalWeight in
both MMR-read paths, since a read can arrive on either.

skins/default/ — the calibrate4 page as page 5 of the calibration flow, and its
registration in standard_includes.tcl.

ScaleTare is not added here. It lives in de1_comms.tcl as set_bengle_scale_tare,
added by the integrated-scale PR, because the ordinary scale tare path needs it whether or
not this wizard ships.

Bounds and status handling

The reference mass is bounded to 1 g – 10 kg, matching decaid and both reaprime skins.
All nine firmware status codes map to distinct messages. The tare step polls for the
firmware's own completion rather than declaring success a fixed delay after the write.
Leaving via Ok aborts a run in progress.

Known issues, not fixed here

Raised by a review of the series, recorded rather than fixed. Not reproduced on hardware.

• The "Page 5 >" button does not call abort_if_running, and enter_page does not
  stop_polling. The 2 Hz update_verify_display timer may survive page exit and can be
  duplicated, each new loop orphaning the previous poll_after_id. Exiting via Ok does
  abort correctly.
• is_bengle_model is evaluated at skin-load time, so on a first-ever connect the page
  may not be registered. Same root cause as in the LED and autonomy PRs.

Impact on a DE1

The package loads and defines a namespace. calibrate4 is reachable only from the Bengle
calibration flow. The two decode branches match addresses a DE1 never reports.

Test plan

• scale_calibration.tcl sources and runs end to end against stubs: page entry,
  reference-mass validation at both bounds and past them, state-word decode, every
  error code, and the tare step.
• Confirm the app starts on a DE1 with the new package loaded and no error.
• TODO (Ben): run all seven steps on a Bengle with a known weight; confirm both cells
  are detected in either order.
• TODO (Ben): abort mid-measurement; confirm the firmware returns to idle.
• TODO (Ben): leave the page mid-run via "Page 5 >" and confirm the poll timer stops —
  this is the known issue above.
• TODO (Ben): verify accuracy against a reference scale.

Testing

Manual verification and a stub harness. There is no automated test coverage for these Tcl
paths in the repo.