docs(adr): supersede ADR-0007, plan OneDev migration

This repo's own hosting, issue tracking, and pull requests move from Gitea
to OneDev (ADR-0029), keeping the Gitea repo as a read-only archive rather
than deleting it. plugins/gitea is unaffected — it continues to ship as a
marketplace product regardless of what this repo hosts itself on.

Records the full execution plan (prerequisites, mirror/issue/PR/release
phases, verification checklist) and updates CONTEXT.md's Issue entry and
AGENTS.md's source-of-truth line to name OneDev instead of Gitea.

ADR: 0029
Refs: ADR-0007
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GGCPJBXPLJP5FprL4C8nu3

docs/adr/0007-gitea-canonical-issue-tracker.md

@@ -1,5 +1,7 @@
 # Gitea is the exclusive issue tracker — file-based fallback removed
 
+**Superseded by:** ADR-0029 (OneDev supersedes Gitea as this repo's canonical forge — this repo's own hosting, issue tracking, and PRs move to OneDev; `gitea/` continues to ship as a marketplace product regardless)
+
 **Supersedes:** ADR-0011 (provider-agnostic issue tracker with file-based default — archived during refactoring)
 
 > **Note on the ADR-0011 number.** Every "ADR-0011" on this page means the *archived* provider-agnostic issue tracker ADR, which no longer exists in `docs/adr/` — it was removed when it was superseded, and the number 0011 was later reused for an unrelated decision, `docs/adr/0011-gitea-skill-deep-modules.md` (the gitea skill's split into deep modules). That file is not the ADR referenced below. The number is not renumbered here: these ADRs are a published record and renumbering would break every citation that already points at either one. The archived text is recoverable from git history.