docs: eFlow is genuinely Planned, and the eos pointer was wrong

[srpatcha]

This repository has three files. The README said:

The code that will become eFlow lives in eos
today, at (not yet started; EoStudio is the host).

The parenthetical contradicts the pointer, and the pointer is wrong. eFlow is not
kernel-adjacent and no part of it belongs in eos. §18 of the v2.0 master design
places it inside EoStudio:

EmbeddedOS Studio
  |-- Project / Board Config
  |-- Code / Debug / Trace
  |-- eFlow visual design
  |-- eAI model tools
  `-- EoSim integration

Planned is correct here, unlike its siblings

I checked all three placeholder repositories. eNet and eSec are empty
repositories sitting over working code in eos — their status was wrong and I
have corrected it (eNet#1, eSec#1). eFlow is different: there is no
implementation anywhere in the platform.

$ grep -rl "eflow" --include=*.py --include=*.c --include=*.ts EoStudio/ ebuild/
(nothing)

So Planned stands. What changes is that the README now says why, rather than
implying work is under way somewhere else.

The design constraint worth recording

§18.1: eFlow should generate/configure standard EmbeddedOS components and
manifests; it should not create an incompatible second runtime.

eFlow draws a graph and emits manifests. It does not execute anything. The moment
it grows its own scheduler or IPC, the platform has two runtimes and every
EmbeddedOS guarantee has to be re-established inside the second one.

§18 makes the same point about its host: "The graphical environment is a client
of the platform toolchain, never a second implementation."

Why nothing should be built yet

eFlow's output is component manifests. That format did not exist until
embeddedos-org/embeddedos-stack#20, which is still in review. Building a graph
editor that emits an undefined format means inventing the format in the editor —
precisely how the second runtime §18.1 forbids gets started.

EoStudio is not a clean client of eBuild yet either. It carried a 588-line second
build system with seventeen backends, none of them ebuild, and its one
reference to the tool was a string that is not valid CLI
(embeddedos-org/EoStudio#24, partially addressed by EoStudio#25).

The README now names three conditions, in order, under which this repository
earns code — so "when do we start eFlow" has an answer rather than being
re-argued.