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/static/calibration.js

@@ -40,9 +40,7 @@
     var offset = obj.offset === undefined ? 0 : obj.offset;
     if (!isFiniteNum(scale) || scale === 0) return null;
     if (!isFiniteNum(offset)) return null;
-    // Commas and quotes would corrupt the CSV export header; drop them here so
-    // every consumer sees an already-safe unit.
-    var unit = String(obj.unit == null ? '' : obj.unit).replace(/[",]/g, '').trim();
+    var unit = String(obj.unit == null ? '' : obj.unit).trim();
     // Cap at MAX_UNIT_LEN UTF-8 bytes, matching both hubs' Normalise() exactly.
     // TextEncoder/TextDecoder are available natively in all modern browsers and
     // Node v11+; no build step or bundler is needed.