Repoint the tree at Sendspin/sendspin-cpp-cli

[chrisuthe]

The repository moved from chrisuthe/sendspin-cpp-cli to Sendspin/sendspin-cpp-cli.
The old URLs redirect, so nothing was broken — but a tree that names its old home is a
tree that goes stale the day the redirect stops. This repoints it.

What changed

39 occurrences of the old owner across 12 files, mechanically:

• README.md — the wiki link and the git clone line.
• docs/wiki/ — every absolute link back into the repository, across all 9 pages plus
  _Sidebar.md. These are absolute rather than relative because the wiki is a separate
  git repository; wiki-internal links are relative and are untouched.
• packaging/sendspin-cli.service.in — the Documentation= line. Verified through
  configure_file: the generated build/sendspin-cli.service carries the new URL.
• scripts/get_started_linux.sh — readonly REPO, which is what the release download,
  the "no releases yet" refusal and the build-from-source pointer are all built from.

Plus one prose correction, in docs/ROADMAP.md's macOS receipt bullet — see below.

What deliberately did not change

• The pkg identifier io.github.chrisuthe.sendspin-cli stays, in all six places it
  appears — the declaration at scripts/build_macos_pkg.sh:73, the independent one at
  .github/workflows/build.yml:661 that exists so an edit to the script cannot go green
  unnoticed, and four mentions in operator-facing text. It is the primary key of an installer
  receipt on every machine that has run the .pkg; changing it does not rename anything, it
  mints a second receipt claiming the same paths and orphans the first. docs/ROADMAP.md
  already decided that on the record and named this exact move as the thing that would not
  shift it. If it is ever to change it wants its own PR and a migration story — a preinstall
  that forgets the old receipt, or an explicit decision to accept the orphan.

  What that bullet could not keep saying is that io.sendspin.* was not this project's to
  take. When the identifier was minted that was true; now the project is in the Sendspin org
  it is not, and the bullet framed the move as hypothetical besides. So it now records the
  thing that actually makes it worth reading: the cheaper option became available and was
  declined on purpose. The decision, the sendspin-cli-not-sendspin-cpp-cli reasoning and
  the ArduinoJson cross-reference are unchanged. scripts/build_macos_pkg.sh's own comment
  needed nothing — it makes no ownership claim, only the orphaning point, which still holds.

• CMakeLists.txt:6's HOMEPAGE_URL is untouched because it is not a stale-owner URL.
  It already names the Sendspin org — it names the wrong repository, the sendspin-cpp
  library rather than this project, having been copied from the FetchContent declaration at
  line 78 with .git stripped. It predates the transfer, so fixing it here would smuggle a
  semantic change (which repository is this project's homepage) into a mechanical rename.
  Nothing consumes it — no include(CPack) anywhere in the tree, and the only
  configure_file substitutes just @SENDSPIN_CLI_INSTALLED_BINARY@ — so it is inert
  metadata today and a separate one-line correction.

• Workflows needed nothing. wiki.yml builds every URL from $GITHUB_REPOSITORY, and
  release.yml from ${{ github.repository }}; no workflow hardcodes the owner. Confirmed
  by reading them rather than assumed.

Verification

• Zero occurrences of chrisuthe/sendspin-cpp-cli remain in the tree. The only remaining
  chrisuthe string is the pkg identifier, deliberately.
• All 11 distinct rewritten URLs return 200 against the new owner. (A twelfth is the literal
  .../releases/download/v$VERSION inside a shell snippet — a placeholder, not a link.)
• scripts/get_started_linux.sh's no-releases path, run live against the new repo, which has
  published no releases: the refusal names Sendspin/sendspin-cpp-cli and points at
  https://github.com/Sendspin/sendspin-cpp-cli#build.
• shellcheck scripts/*.sh clean — CI's own gate.
• Build and tests: 347/347 pass. Worth knowing for anyone reproducing in a deep directory —
  ConfigMerge.AConfiguredControlSocketIsAbsolutizedUnderDaemonize fails when the build
  directory's absolute path is long enough to push the absolutized socket path past the
  103-byte sockaddr_un limit (105 bytes here). The same binary passes 347/347 from a short
  cwd. Nothing in this diff is C++ or CMake.

The wiki

The sync workflow ran on the current main (a55a67a) and published successfully. That
run is timestamped before the transfer, so it pushed to the wiki under the old name — which
GitHub carried across with the repository. Wikis are enabled on the new repo and the wiki
repository exists, so no owner toggle is needed here: merging this re-syncs the pages with
the corrected links on the next push to main.