refactor: split http/mcp/story_tools.rs into 5 sub-modules by item type

The 1864-line story_tools.rs is split into:

- story.rs: story creation/lifecycle/management (903 lines incl. tests)
- criteria.rs: acceptance-criteria tools (534 lines)
- bug.rs: bug item tools (318 lines)
- spike.rs: spike item tools (120 lines)
- refactor.rs: refactor item tools (60 lines)
- mod.rs: re-exports (25 lines)

Tests stay co-located with the code they exercise; setup_git_repo_in and
setup_story_for_update test helpers are duplicated into the modules that need
them rather than centralised, since they are tiny and test-only.

No behaviour change. All 60 story_tools tests pass; full suite green
(2635 tests with --test-threads=1).

server/src/http/mcp/story_tools/refactor.rs

@@ -0,0 +1,60 @@
+//! Refactor item MCP tools.
+
+use crate::agents::{
+    close_bug_to_archive, feature_branch_has_unmerged_changes, move_story_to_done,
+};
+use crate::http::context::AppContext;
+use crate::http::workflow::{
+    add_criterion_to_file, check_criterion_in_file, create_bug_file, create_refactor_file,
+    create_spike_file, create_story_file, edit_criterion_in_file, list_bug_files,
+    list_refactor_files, load_pipeline_state, load_upcoming_stories, remove_criterion_from_file,
+    update_story_in_file, validate_story_dirs,
+};
+use crate::io::story_metadata::{
+    check_archived_deps, check_archived_deps_from_list, parse_front_matter, parse_unchecked_todos,
+};
+use crate::service::story::parse_test_cases;
+use crate::slog_warn;
+#[allow(unused_imports)]
+use crate::workflow::{TestCaseResult, TestStatus, evaluate_acceptance_with_coverage};
+use serde_json::{Value, json};
+use std::collections::HashMap;
+use std::fs;
+
+
+pub(crate) fn tool_create_refactor(args: &Value, ctx: &AppContext) -> Result<String, String> {
+    let name = args
+        .get("name")
+        .and_then(|v| v.as_str())
+        .ok_or("Missing required argument: name")?;
+    let description = args.get("description").and_then(|v| v.as_str());
+    let acceptance_criteria: Option<Vec<String>> = args
+        .get("acceptance_criteria")
+        .and_then(|v| serde_json::from_value(v.clone()).ok());
+    let depends_on: Option<Vec<u32>> = args
+        .get("depends_on")
+        .and_then(|v| serde_json::from_value(v.clone()).ok());
+
+    let root = ctx.state.get_project_root()?;
+    let refactor_id = create_refactor_file(
+        &root,
+        name,
+        description,
+        acceptance_criteria.as_deref(),
+        depends_on.as_deref(),
+    )?;
+
+    Ok(format!("Created refactor: {refactor_id}"))
+}
+
+pub(crate) fn tool_list_refactors(ctx: &AppContext) -> Result<String, String> {
+    let root = ctx.state.get_project_root()?;
+    let refactors = list_refactor_files(&root)?;
+    serde_json::to_string_pretty(&json!(
+        refactors
+            .iter()
+            .map(|(id, name)| json!({ "refactor_id": id, "name": name }))
+            .collect::<Vec<_>>()
+    ))
+    .map_err(|e| format!("Serialization error: {e}"))
+}