refactor: split http/workflow/story_ops.rs (1256) into create + criterion + update

The 1256-line story_ops.rs is split:

- create.rs: create_story_file + tests (~232 lines)
- criterion.rs: check/add/remove/edit_criterion_in_file + tests (~525 lines)
- update.rs: update_story_in_file + yaml helpers + tests (~640 lines)
- mod.rs: re-exports (~12 lines)

Workflow helpers (read_story_content, write_story_content, slugify_name, etc.)
bumped from pub(super) to pub(crate) since they're now consumed across nested
sub-modules and from http/mcp/story_tools/.

Tests stay co-located. All 2636 tests pass; clippy clean.

server/src/http/workflow/mod.rs

@@ -300,13 +300,13 @@ pub fn validate_story_dirs(_root: &std::path::Path) -> Result<Vec<StoryValidatio
 /// Read story content from the database content store.
 ///
 /// Returns the story content or an error if not found.
-pub(super) fn read_story_content(_project_root: &Path, story_id: &str) -> Result<String, String> {
+pub(crate) fn read_story_content(_project_root: &Path, story_id: &str) -> Result<String, String> {
     crate::db::read_content(story_id)
         .ok_or_else(|| format!("Story '{story_id}' not found in any pipeline stage."))
 }
 
 /// Write story content to the DB content store and CRDT.
-pub(super) fn write_story_content(
+pub(crate) fn write_story_content(
     _project_root: &Path,
     story_id: &str,
     stage: &str,
@@ -316,7 +316,7 @@ pub(super) fn write_story_content(
 }
 
 /// Determine what stage a story is in (from CRDT).
-pub(super) fn story_stage(story_id: &str) -> Option<String> {
+pub(crate) fn story_stage(story_id: &str) -> Option<String> {
     crate::pipeline_state::read_typed(story_id)
         .ok()
         .flatten()
@@ -328,7 +328,7 @@ pub(super) fn story_stage(story_id: &str) -> Option<String> {
 /// Finds the first occurrence of `## {section_name}` and replaces everything
 /// until the next `##` heading (or end of file) with the provided text.
 /// Returns an error if the section is not found.
-pub(super) fn replace_section_content(
+pub(crate) fn replace_section_content(
     content: &str,
     section_name: &str,
     new_text: &str,
@@ -381,7 +381,7 @@ pub(super) fn replace_section_content(
 /// The new section is placed immediately before the first occurrence of
 /// `## {before_section}`.  If `before_section` is `None` or not found in the
 /// document, the section is appended at the end.
-pub(super) fn create_section_content(
+pub(crate) fn create_section_content(
     content: &str,
     section_name: &str,
     new_text: &str,
@@ -468,7 +468,7 @@ pub(super) fn replace_or_append_section(contents: &str, header: &str, new_sectio
     }
 }
 
-pub(super) fn slugify_name(name: &str) -> String {
+pub(crate) fn slugify_name(name: &str) -> String {
     let slug: String = name
         .chars()
         .map(|c| {
@@ -501,7 +501,7 @@ pub(super) fn slugify_name(name: &str) -> String {
 }
 
 /// Get the next available item number from the database/CRDT.
-pub(super) fn next_item_number(_root: &std::path::Path) -> Result<u32, String> {
+pub(crate) fn next_item_number(_root: &std::path::Path) -> Result<u32, String> {
     Ok(crate::db::next_item_number())
 }