feat(ansible): structured playbook-variable fields on the schedule form

The Ansible Schedules form only offered a free-form extra-vars textarea,
unlike the browse/host run forms which auto-populate a field per declared
playbook variable (vars:/vars_prompt:) plus the playbook description. Wire
the schedule form to the same shared `_playbook_vars.html` partial:

- Playbook <select> now loads /ansible/playbook-vars?schedule=1 on change
  into a #sch-playbook-vars container (mirrors the host detail form).
- Edit mode pre-renders the saved playbook's variables server-side with
  their stored values; the extra-vars textarea keeps only leftover
  (non-declared) vars.
- Partial gains optional `values` (prefill) and `schedule` flags. In the
  schedule context secret vars render disabled ("secrets can't be
  scheduled") since they're dropped downstream, and the destructive-confirm
  gate is shown but not required.

Backend already parsed var__* fields for schedules, so this is the
front-end/partial parity fix.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

steward/ansible/routes.py

@@ -172,6 +172,8 @@ async def playbook_vars():
     (vars/vars_prompt), loaded when a playbook is chosen from a dropdown."""
     source_name = (request.args.get("source_name", "") or "").strip()
     playbook_path = (request.args.get("playbook_path", "") or "").strip()
+    # Schedule form: schedules can't prompt, so secret vars render disabled.
+    schedule = (request.args.get("schedule", "") or "").strip() == "1"
     source = next((s for s in _get_sources() if s["name"] == source_name), None)
     variables: list = []
     meta: dict = {"description": "", "category": "", "confirm": False}
@@ -182,7 +184,8 @@ async def playbook_vars():
             meta = src_module.discover_playbook_meta(contents)
     return await render_template(
         "ansible/_playbook_vars.html", variables=variables,
-        description=meta["description"], category=meta["category"], confirm=meta["confirm"])
+        description=meta["description"], category=meta["category"],
+        confirm=meta["confirm"], schedule=schedule)
 
 
 @ansible_bp.get("/run-form/<source_name>/<path:playbook_path>")
@@ -383,11 +386,25 @@ async def schedules():
         if editing_id and s.id == editing_id:
             editing = s
 
+    # Edit mode: pre-render the selected playbook's declared variables so their
+    # saved values show (fresh loads fetch these via HTMX from /playbook-vars).
+    edit_variables: list = []
+    edit_meta: dict = {"description": "", "category": "", "confirm": False}
+    if editing:
+        src = next((s for s in _get_sources() if s["name"] == editing.source_name), None)
+        if src:
+            contents = src_module.read_playbook(src["path"], editing.playbook_path)
+            if contents is not None:
+                edit_variables = src_module.discover_playbook_variables(contents)
+                edit_meta = src_module.discover_playbook_meta(contents)
+
     return await render_template(
         "ansible/schedules.html",
         rows=rows, groups=groups, targets=targets,
         source_data=source_data, all_playbooks=all_playbooks,
         editing=editing, interval_presets=INTERVAL_PRESETS,
+        edit_variables=edit_variables, edit_description=edit_meta["description"],
+        edit_category=edit_meta["category"], edit_confirm=edit_meta["confirm"],
     )