docs: standardize GitHub workflow and CI policy

.github/PULL_REQUEST_TEMPLATE.md

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+## Change summary
+
+- Area: research-core | research-standards | theory-history | book-writing | thai-policy | services-tools | repo-ops | other
+- Canonical workspace/path:
+- What changed:
+- Why this change is needed:
+
+## Evidence and validation
+
+- Checks actually run:
+- Result or artifact produced:
+- Claim/readiness impact:
+- Next blocker or follow-up:
+
+## Public boundary
+
+- [ ] No .env, credentials, private exports, raw media, build cache, binary, or generated database is included.
+- [ ] Any excluded raw/private input is named in a manifest or ledger entry when needed.
+- [ ] No duplicate semantic path or stale alias was created.
+- [ ] git diff --check was run.
+
+## Work history
+
+- [ ] A factual WORK_LEDGER/YYYY/YYYY-MM-DD.md entry was added.
+- [ ] The relevant topic/book UPDATE_LOG.md was updated, or this change does not require one.
+- [ ] The staged file list is limited to this coherent unit.
+
+## Merge readiness
+
+- [ ] This PR is ready to merge.
+- [ ] This PR should remain a draft.