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/kyberforge/skills/agent-author/scripts/new-agent.sh

@@ -17,7 +17,7 @@ Arguments:
                 plugin scope  : root contains plugin.json
                                → creates <root>/agents/<name>.md
                                → creates <root>/agents/<name>.agent.md
-                               → creates <root>/agents/sources.md (if absent)
+                               → creates <root>/sources.md (if absent)
                 project scope : root is a project directory (no plugin.json)
                                → creates <root>/.claude/agents/<name>.md
                                → creates <root>/.github/agents/<name>.agent.md
@@ -86,7 +86,7 @@ case "$SCOPE" in
   plugin)
     CC_DIR="$ROOT/agents"
     CP_DIR="$ROOT/agents"
-    SOURCES_DIR="$ROOT/agents"
+    SOURCES_DIR="$ROOT"
     ;;
   project)
     CC_DIR="$ROOT/.claude/agents"