Add thread section management APIs (#36380)

## What changed

- Add `threadSection/create`, `threadSection/update`, and `threadSection/delete` app-server methods, with generated protocol schemas and TypeScript bindings.
- Persist custom sections in SQLite with stable UUIDv7 identities, trim and validate display names, and prevent renaming or deleting the built-in pinned section.
- Delete sections transactionally and return their active and archived threads to the unsectioned list.
- Serialize section mutations with section listing so concurrent requests observe ordered updates.

## Testing

- Cover section persistence across restarts, ordered renames, member cleanup on deletion, invalid requests, unsupported stores, and thread-store/state-runtime behavior.

GitOrigin-RevId: dc9a4be283c21dbc93ab1829eafc4825d8df6575

codex-rs/thread-store/src/thread_sections.rs

@@ -0,0 +1,49 @@
+/// Parameters for listing independently persisted thread sections.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct ListThreadSectionsParams {
+    /// Opaque cursor returned by a previous section listing.
+    pub cursor: Option<String>,
+    /// Maximum number of sections to return.
+    pub limit: usize,
+}
+
+/// Parameters for creating a thread section.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct CreateThreadSectionParams {
+    /// User-facing section name.
+    pub name: String,
+}
+
+/// Parameters for renaming a thread section.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct RenameThreadSectionParams {
+    /// Stable identifier of the section to rename.
+    pub section_id: String,
+    /// Replacement user-facing section name.
+    pub name: String,
+}
+
+/// Parameters for deleting a thread section.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct DeleteThreadSectionParams {
+    /// Stable identifier of the section to delete.
+    pub section_id: String,
+}
+
+/// An independently persisted thread section and its user-facing name.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct StoredThreadSection {
+    /// Stable, server-owned section identifier.
+    pub id: String,
+    /// User-facing section name.
+    pub name: String,
+}
+
+/// A cursor-paginated page of independently persisted thread sections.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct StoredThreadSectionsPage {
+    /// Sections returned for this page.
+    pub sections: Vec<StoredThreadSection>,
+    /// Opaque cursor to continue listing sections.
+    pub next_cursor: Option<String>,
+}