docs: document TQL CTE support in CREATE FLOW

[Copilot]

Documents the new TQL CTE pattern for CREATE FLOW introduced in GreptimeTeam/greptimedb#7702, which allows wrapping TQL EVAL in a CTE for cleaner flow definitions and stable output column names.

What's Changed in this PR

• docs/user-guide/flow-computation/continuous-aggregation.md — Added "Wrapping TQL with a CTE" section covering syntax, use case (column renaming before sink table schema inference), and supported shape restrictions
• docs/reference/sql/create.md — Extended CREATE FLOW section with the TQL CTE form and its strict shape requirements
• docs/user-guide/query-data/cte.md — Added key point noting that TQL CTEs in CREATE FLOW only support the simplest form (single CTE + SELECT *)
• All changes mirrored in i18n/zh/ (Chinese) and versioned_docs/version-1.0/

The supported syntax:

CREATE FLOW calc_rate_cte
SINK TO rate_reqs_cte
EVAL INTERVAL '1m' AS
WITH rate_data (ts, req_rate, host, job, instance) AS (
    TQL EVAL (now() - '1m'::interval, now(), '30s')
    rate(http_requests_total{job="my_service"}[1m])
    AS req_rate
)
SELECT * FROM rate_data;

Restrictions: exactly one TQL CTE, outer query must be SELECT * FROM <cte-name>, no WHERE/joins/projections/extra CTEs. Quoted CTE names must be referenced consistently.

Checklist

• Please confirm that all corresponding versions of the documents have been revised.
• Please ensure that the content in sidebars.ts matches the current document structure when you changed the document structure.
• This change requires follow-up update in localized docs.

[discord9]

if diff is actually added then LGTM