docs(provenance): migrate the corpus to the Research registry grammar

Repoint every `Research doc:` at the plugin's Research registry
(git/sources.md, pre-commit/sources.md, gitea/sources.md,
agentsmd/sources.md), keeping the old topic-doc link as a parenthetical
`(digest: ...)` annotation. Brace expansions and the gitea-releases
semicolon pair collapse to one path.

Entries with no registry (org-commit-conventions, org-git-conventions,
governance-secrets-hard-prohibition, adr-0002-0003-two-tier-claude-md)
now declare `none` plus `Basis:` bullets. The two git entries cite
core/instructions/git.md and commits.md as `(removed in 5deed07)`.

Remove the house-vale-3-15-2-repro entry and its source_keys citations
from vale-config and vale-run. It claimed six behaviours were reproduced
against purpose-built fixtures in this repo, but the entry was added in
d1afdbe with no test or fixture files, and none exists in history. The
behavioural rules stay; only the unbacked provenance claim goes.

Refs: #121
ADR: 0028
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EGHFJextYtVQseaHPDDhxB

plugins/core/.apm/skills/agentsmd-audit/references/sources.md

@@ -28,6 +28,7 @@
 
 - **URL:** (org convention — not a plugin research corpus entry)
 - **Description:** Hard prohibition on placing secrets, API keys, tokens, or credentials in code, config, prompts, or any output. Grounds the secrets/credentials check in `scripts/validate-secrets.sh` and Step 1 of SKILL.md — AGENTS.md is committed content, so an embedded real secret is a hard-prohibition violation, not a style nit.
-- **Research doc:** core/instructions/governance.md (org convention file, not a plugin research corpus entry; content is inlined here since plugins must be self-contained and this file may not exist wherever the plugin is installed)
+- **Research doc:** none — org convention, not a plugin research corpus entry
+- **Basis:** core/instructions/governance.md (content is inlined here since plugins must be self-contained and this file may not exist wherever the plugin is installed)
 - **Contributing files:** SKILL.md
 - **Status:** `extracted`