feat(cli): expose available_statuses in robot mode and hide status_category

(Supersedes empty commit f3788eb — jj auto-snapshot race.)

Three related refinements to how work item status is presented:

1. available_statuses in meta (list.rs, main.rs):
   Robot-mode issue list responses now include meta.available_statuses —
   a sorted array of all distinct status_name values in the database.
   Agents can use this to validate --status filter values or display
   valid options without a separate query.

2. Hide status_category from JSON (list.rs, show.rs):
   status_category is a GitLab internal classification that duplicates
   the state field. Switched to skip_serializing so it never appears
   in JSON output while remaining available internally.

3. Simplify human-readable status display (show.rs):
   Removed the "(category)" parenthetical from the Status line.

4. robot-docs schema updates (main.rs):
   Documented --status filter semantics and meta.available_statuses.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/cli/commands/list.rs

@@ -59,7 +59,7 @@ pub struct IssueListRow {
     pub unresolved_count: i64,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub status_name: Option<String>,
-    #[serde(skip_serializing_if = "Option::is_none")]
+    #[serde(skip_serializing)]
     pub status_category: Option<String>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub status_color: Option<String>,
@@ -86,7 +86,7 @@ pub struct IssueListRowJson {
     pub project_path: String,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub status_name: Option<String>,
-    #[serde(skip_serializing_if = "Option::is_none")]
+    #[serde(skip_serializing)]
     pub status_category: Option<String>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub status_color: Option<String>,
@@ -124,6 +124,7 @@ impl From<&IssueListRow> for IssueListRowJson {
 pub struct ListResult {
     pub issues: Vec<IssueListRow>,
     pub total_count: usize,
+    pub available_statuses: Vec<String>,
 }
 
 #[derive(Serialize)]
@@ -268,10 +269,21 @@ pub fn run_list_issues(config: &Config, filters: ListFilters) -> Result<ListResu
     let db_path = get_db_path(config.storage.db_path.as_deref());
     let conn = create_connection(&db_path)?;
 
-    let result = query_issues(&conn, &filters)?;
+    let mut result = query_issues(&conn, &filters)?;
+    result.available_statuses = query_available_statuses(&conn)?;
     Ok(result)
 }
 
+fn query_available_statuses(conn: &Connection) -> Result<Vec<String>> {
+    let mut stmt = conn.prepare(
+        "SELECT DISTINCT status_name FROM issues WHERE status_name IS NOT NULL ORDER BY status_name",
+    )?;
+    let statuses = stmt
+        .query_map([], |row| row.get::<_, String>(0))?
+        .collect::<std::result::Result<Vec<_>, _>>()?;
+    Ok(statuses)
+}
+
 fn query_issues(conn: &Connection, filters: &ListFilters) -> Result<ListResult> {
     let mut where_clauses = Vec::new();
     let mut params: Vec<Box<dyn rusqlite::ToSql>> = Vec::new();
@@ -457,6 +469,7 @@ fn query_issues(conn: &Connection, filters: &ListFilters) -> Result<ListResult>
     Ok(ListResult {
         issues,
         total_count,
+        available_statuses: Vec::new(),
     })
 }
 
@@ -822,11 +835,13 @@ pub fn print_list_issues(result: &ListResult) {
 
 pub fn print_list_issues_json(result: &ListResult, elapsed_ms: u64, fields: Option<&[String]>) {
     let json_result = ListResultJson::from(result);
-    let meta = RobotMeta { elapsed_ms };
     let output = serde_json::json!({
         "ok": true,
         "data": json_result,
-        "meta": meta,
+        "meta": {
+            "elapsed_ms": elapsed_ms,
+            "available_statuses": result.available_statuses,
+        },
     });
     let mut output = output;
     if let Some(f) = fields {