fix(dmx-driver): accept a signed inputs word so bit 31 stops freezing the lights

[groupsky]

Fixes #1586.

The bug

message-handler.js rejected any reading whose inputs field was negative. But
inputs from the mbsl32di driver is a signed 32-bit word — built as
data[1] << 16 | data[0], so it is negative exactly when input bit 31 is closed.
Bit 31 is a door contact in production, so whenever that one door was in that
state the driver dropped every dry-switch reading and all three bath door
indicators froze at their last frame.

On routy the universe sat at [0, 0, 128] from 2026-09-09T05:22:06Z: 305
readings dropped, 145 frames written, last frame 05:21:31Z. Sample dropped
reading: {"inputs":-39828385, ...} — (-39828385) >>> 0 is
0b11111101101000000100010001011111, a perfectly valid word with bit 31 set.

Introduced by c92cae9 (#1543). That hardening was right to reject Infinity and
fractional values; the < 0 clause overreached — its rationale assumed -1 and
did not account for bit 31 being a used input on a 32-input module.

The fix

Accept the full 32-bit range, signed or unsigned, and normalise with >>> 0
before the bit tests — the same thing docker/mqtt-influx/converters/mbsl32di.js
already does.

• Number.isSafeInteger still closes Infinity (reachable from JSON as 1e999)
  and fractional values.
• The range check now closes only values genuinely outside 32 bits, which the
  bitwise operators would otherwise wrap into a different reading.
• A negative inputs is now a normal reading. -1 is all 32 inputs closed.
• The drop log said "unsigned integer inputs field", which no longer describes
  the guard; it now names the 32-bit range.

dmx-driver was the only service carrying the < 0 clause; the other sites
touched by c92cae9 are unaffected.

Tests

Written first, watched fail, then fixed — the four new negative/range cases
failed against the old guard for exactly the expected reasons.

• the production reading -39828385 drives the channels instead of being dropped
• -2147481056 (every mapped bit closed and bit 31) lights all three channels
• -1 is all inputs closed, not a malformed reading
• 4294967296 and -2147483649 are still dropped, universe untouched
• the drop log names the range it enforced
• Infinity/1e999 and fractional values still dropped (unchanged)

The obsolete drops a negative inputs field rather than lighting every channel
test encoded the bug and is replaced by the out-of-range cases.

$ npm ci --ignore-scripts && npm test
Test Suites: 2 passed, 2 total
Tests:       26 passed, 26 total

Done when

• message-handler.js accepts a reading with bit 31 set and drives channels 1-3 from its bits
• Infinity, 1e999, fractional and out-of-32-bit-range values are still dropped, universe untouched
• Regression test covering a negative inputs (-39828385) asserting the expected channel levels
• npm test green in docker/dmx-driver/
• docker/dmx-driver/CLAUDE.md corrected
• Deployed to routy; docker logs homy-dmx-driver-1 shows frames written with no "Ignoring payload" lines for well-formed readings
• Locking a bath visibly changes the light on its door

https://claude.ai/code/session_01DAyhJDqko1EAvddsatHRDo