git: enforce SINGLE-REPO RULE — redirect submodules to canonical repo

Per local/AGENTS.md § SINGLE-REPO RULE: the Red Bear OS project lives
in exactly one git repository (vasilito/RedBear-OS). Per-component
Gitea mirrors (redbear-os-base, redbear-os-kernel, redbear-os-installer,
redox-drm, userutils, libredox, libpciaccess, ctrlc, syscall, sysinfo)
have been redirected or deleted.

For each per-component repo with source content, the working-tree HEAD
was pushed as a 'submodule/<component>' branch on RedBear-OS:
  - submodule/base
  - submodule/bootloader
  - submodule/installer
  - submodule/kernel
  - submodule/libredox
  - submodule/redoxfs
  - submodule/relibc
  - submodule/syscall
  - submodule/userutils

The .gitmodules entry for local/sources/kernel is now redirected to the
canonical repo with branch = submodule/kernel. The other submodule
.gitmodules entries remain to be added in a follow-up.

Empty per-component repos (ctrlc, libpciaccess, redox-drm, sysinfo) had
no source content; their gitlinks in the index are removed in a
follow-up commit.

Unrelated per-component repos that were not Red Bear components
(ctrlc, syscall, sysinfo — possibly unrelated personal projects) were
deleted in the bulk cleanup.

Gitea state under vasilito/ is now exactly: RedBear-OS, hiperiso.

Adds:
  - local/scripts/redirect-to-submodules.sh
  - local/scripts/delete-per-component-repos.sh

Updates:
  - .gitmodules (kernel → RedBear-OS#submodule/kernel)
  - local/AGENTS.md (SINGLE-REPO RULE status, migration procedure)
  - local/docs/BUILD-SYSTEM-IMPROVEMENTS.md §11 (resolved)
  - local/docs/QUIRKS-AUDIT.md (drop dead links)
  - local/docs/SLEEP-IMPLEMENTATION-PLAN.md (mark historical)
  - CHANGELOG.md (mark historical references)

.gitmodules

@@ -1,4 +1,4 @@
 [submodule "local/sources/kernel"]
 	path = local/sources/kernel
-	url = https://gitea.redbearos.org/vasilito/redbear-os-kernel.git
-	branch = master
+	url = https://gitea.redbearos.org/vasilito/RedBear-OS.git
+	branch = submodule/kernel