Rules: Update GitHub issue description writing rules

Signed-off-by: Michael Mayer <michael@photoprism.app>

.claude/rules/commit-and-docs-style.md

@@ -17,6 +17,7 @@ Do not add `Co-Authored-By: Claude …` trailers (or any other AI-authorship tra
 Issue titles MUST be concise, use the imperative mood, and start with a single capitalized prefix followed by a colon and a space, e.g. `Search: Add filter for RAW image formats`.
 
 Issue descriptions MUST begin with a one-sentence **User Story** in the format: `**As a <role>, I want <goal>, so that <outcome>.**`
+Use level-4 Markdown headings for sections within issue descriptions, for example `#### Acceptance Criteria`.
 Follow the User Story with a clear summary of the expected behavior, rationale, technical considerations, and constraints.
 
 Descriptions MUST conclude with a checklist of **Acceptance Criteria**:

AGENTS.md

@@ -51,6 +51,7 @@ Optional nested repositories such as `plus/`, `pro/`, `portal/`, and `specs/` ma
 
 - Titles must be concise, imperative, and start with one capitalized prefix plus `: `, for example `Search: Add filter for RAW image formats`.
 - Descriptions must begin with a one-sentence bold user story: `**As a <role>, I want <goal>, so that <outcome>.**`
+- Use level-4 Markdown headings for sections within issue descriptions, for example `#### Acceptance Criteria`.
 - Follow with behavior, rationale, technical considerations, and constraints.
 - End with `- [ ]` checklist items for the acceptance criteria, each using `MUST`, `SHOULD`, or `MAY`.
 - Agents may create, edit, close, reopen, relabel, or otherwise modify GitHub issues only when explicitly requested by the user.