docs: close Gate 2 - sources taxonomy, upstream drift check, ADRs accepted

Amendments decided with the human at the Gate-2 STOP: docs/sources/
gets a by-source-type taxonomy (regelwerk/upstream/protokolle/
migration, proposed by sorb), the pinned v0.1.1 originals become a
byte-compare baseline against silent framework-file rewrites, AGENTS.md
carries the change-only-with-sorb rule forward, and the issue import
may read descriptions via the token (read-only). ADR-0011 and ADR-0012
flipped to accepted.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/adr/0011-issues-im-repo-gitlab-als-spiegel.md

@@ -1,7 +1,7 @@
 ---
 type: adr
 id: "0011"
-status: proposed
+status: accepted
 date: 2026-08-11
 supersedes: null
 superseded_by: null

docs/adr/0012-gruppenregeln-kanonisch-mit-pruefung.md

@@ -1,7 +1,7 @@
 ---
 type: adr
 id: "0012"
-status: proposed
+status: accepted
 date: 2026-08-11
 supersedes: null
 superseded_by: null