Restore calibration parity: revert unit-stripping from normaliseCal, fix CSV quoting at export

Finding 1: revert the comma/quote strip added in 3cb998c from
normaliseCal() in calibration.js. The strip broke byte-identical parity
with Go CalConfig.Normalise and C++ StreamHub::SetCalibrationEntry, both
of which only trim whitespace and cap at 16 UTF-8 bytes. Delete the
companion test that asserted the now-removed behaviour (suite returns to
18 tests).

Finding 2: fix the actual CSV-safety problem at the point of use in
exportAllCSV() in app.js. Header cells (time column and signal columns)
are now RFC 4180-quoted: wrapped in double quotes with any embedded
double quote doubled. This safely handles units or signal names that
contain commas or quotes without touching normaliseCal.

Finding 3: update two stale comments in app.js that called the trigger
threshold or rawFromNorm result 'raw' — Task 9 moved trig.threshold into
calibrated units throughout, so the comments now say 'calibrated'.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Client/udpstreamer/test/calibration.test.js

@@ -150,7 +150,3 @@ test('CalTable.list is sorted by source then signal', () => {
   assert.deepStrictEqual(t.list().map(e => e.source + '/' + e.signal),
                          ['a/b', 'a/z', 'z/a']);
 });
-
-test('normaliseCal strips characters that would corrupt a CSV header', () => {
-  assert.strictEqual(C.normaliseCal({source: 'w', signal: 's', unit: 'k,V"'}).unit, 'kV');
-});