fix(agents): relocate provenance sources.md outside agents/ dir

`claude plugin validate --strict` auto-discovers every .md under a
plugin's agents/ directory as an agent requiring frontmatter, so the
provenance file there always needs fake agent frontmatter to pass
validation. Confirmed empirically that an explicit `agents` manifest
array can't suppress this discovery. Move the file to <plugin-root>/
sources.md instead, and update agent-author/agent-audit accordingly.

Adds ADR-0010, partially superseding ADR-0005's `agents/sources.md`
convention. Fixes #63.

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

plugins/git/agents/sources.md

@@ -1,55 +0,0 @@
----
-name: git-agents-sources
-description: Provenance record for the git plugin's agents, not an invokable agent. Do not invoke.
-tools: none
----
-
-# Sources
-
-## context7-git-htmldocs
-
-- **URL:** context7:/git/htmldocs
-- **Research doc:** plugins/git/docs/research/docs/git/sources.md
-- **Description:** Official Git HTML documentation from the git/htmldocs repository — covers all commands, concepts, and internals.
-- **Contributing files:** agents/git-orchestrate.md, agents/git-orchestrate.agent.md
-- **Status:** `extracted`
-
-## git-scm-docs
-
-- **URL:** https://git-scm.com/docs/git-config
-- **Research doc:** plugins/git/docs/research/docs/git/sources.md
-- **Description:** Official git-scm.com reference pages — git-config manual and CLI reference.
-- **Contributing files:** agents/git-orchestrate.md, agents/git-orchestrate.agent.md
-- **Status:** `extracted`
-
-## git-scm-worktree-docs
-
-- **URL:** https://git-scm.com/docs/git-worktree
-- **Research doc:** plugins/git/docs/research/docs/git/sources.md
-- **Description:** Official git-scm.com reference for git-worktree — subcommands, flags, ref-sharing rules.
-- **Contributing files:** agents/git-orchestrate.md, agents/git-orchestrate.agent.md
-- **Status:** `extracted`
-
-## git-scm-submodule-docs
-
-- **URL:** https://git-scm.com/docs/git-submodule
-- **Research doc:** plugins/git/docs/research/docs/git/sources.md
-- **Description:** Official git-scm.com reference for git-submodule — subcommands, flags, configuration keys.
-- **Contributing files:** agents/git-orchestrate.md, agents/git-orchestrate.agent.md
-- **Status:** `extracted`
-
-## git-scm-remote-docs
-
-- **URL:** https://git-scm.com/docs/git-remote
-- **Research doc:** plugins/git/docs/research/docs/git/sources.md
-- **Description:** Official git-scm.com reference for git-remote — add, remove, rename, set-url, prune.
-- **Contributing files:** agents/git-orchestrate.md, agents/git-orchestrate.agent.md
-- **Status:** `extracted`
-
-## conventional-commits-spec
-
-- **URL:** https://www.conventionalcommits.org/en/v1.0.0/
-- **Research doc:** plugins/git/docs/research/docs/git/sources.md
-- **Description:** The Conventional Commits v1.0.0 specification — format rules, breaking change conventions, footer token format.
-- **Contributing files:** agents/git-orchestrate.md, agents/git-orchestrate.agent.md
-- **Status:** `extracted`