Let the roadmap be what is open, and the code keep its reasons

[AndreasBur]

The file was 712 lines, and every one of the six numbered sections plus eight of the
thirteen backlog items were marked Done. So it was a changelog with a plan inside it —
and the two read in opposite directions: a plan from the front, a changelog not at all.
Finding the five open items meant reading past 57 % of the file.

What actually made it long

Not the Done markers. The reasoning was written twice:

Decision	Where it already was	Where it was told again
Why the supply switch is a task, not two lines	Power.h, file \details	roadmap section 6
Why blanking alone would not keep the line quiet	Power.h	roadmap section 6
Why the hue is not stored	ColorCycle.h, 142 lines of \details	backlog item 5
Why the limiter asks what is shown	Display.cpp, at getCurrentLimit()	backlog item 5
Why the night acts on the crossing	NightSwitch.h	backlog item 2
Why the stored text is a fixed field	Persistence.h	roadmap section 2
Why a restart is asked for, not taken	the RPC parser, at the case	roadmap section 5

The code's version is the better one — it is at the function, in its own words, where
somebody changing that function will read it. The roadmap's copy could only fall behind.
So the finished items are now one line and a link each, pointing at the header that
explains them.

Every rationale was checked against the tree before its copy was removed. Eighteen
were searched for; the four a literal search missed were read by hand, and all four are
at their function — Version.h carries "a build that wants to say more overrides it from
the outside", Display::toggle() carries "for a button that has nothing to read the state
off", and so on. Nothing was deleted on the assumption that it must be somewhere.

Three things had no such home, so they moved

• docs/decisions.md — the measurement that ended the Fast accessor pair. It is a
  property of a pattern spanning the whole tree, not of a class, and no header owns it.
  The platform contract already referred to it by backlog number ("the roadmap's backlog
  item 9"), which this restructure would have broken; it points at a stable anchor now.
• docs/comparison.md — wordclock24h, ESPWortuhr and ednieuw, what each contributed,
  and "where this project is ahead". A yardstick does not change when work gets done, so
  it does not belong in a file that changes every time something ships.
• docs/serial-commands.md — "Adding an RPC" is an instruction for somebody adding a
  command, which is what that document is for. Two sentences were added from section 4
  while it moved: ids 22–30 can be refused and carry a code, ids 34–40 cannot and all
  answer Error=0.

What the roadmap says now

136 lines. Three items next (Bluetooth transport, MQTT/Home Assistant, Ambilight), two
waiting on a board (RMT by DMA, and watching an OTA image actually be applied — the
handler is exercised against stand-ins, the loader has never been seen booting into
something it was sent), one waiting on https, one idea that needs a second front plate
before it is a plan, and the "deliberately not planned" list.

Checks

Documentation only — git diff --name-only is seven .md files. Every relative link in
the touched files was resolved against the working tree, and the #the-fast-accessor-pair
anchor against its heading. tools/documented-sizes.py passes; no new size claim was
added, and the existing ones were left exactly as written, because they describe changes
that were made and this repository's rule is that such a number is history.