fix(pgwire): answer kv writes with one INSERT tag

[EnRaiha]

Why

Key-value writes answered a bare OK command tag: an INSERT or PUT against a kv collection reported no affected count, so drivers saw an empty tag where INSERT 0 1 is expected. The count-bearing tag semantics are the kv half of #297.

What

• data/executor/handlers/kv/crud/write_basic.rs: kv Put and Insert answer through response_affected(task, 1) — the write reports the row it wrote instead of a bare OK.
• response_shape/types/plan_kind.rs: KvOp::Insert, KvOp::Put, and KvOp::BatchPut classify as DmlResult("INSERT"), so the routed response renders INSERT 0 1 rather than an execution tag.
• The wire case extends sql_dml_affected_counts with the kv INSERT/PUT counts.

Refs #297.

Validation

• cargo check -p nodedb --all-targets — clean (rebased on current main).
• cargo test -p nodedb --test wire sql_dml_affected_counts — 16 passed.
• Repository preflight passes.

Notes

• The earlier revision of this PR also carried the routed shaper SQLSTATE work; that content now lives in its own PR (fix(pgwire): classify the streamed and DDL shaping failures #341).

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[farhan-syah]

Superseded by #356, which carries the kv INSERT/PUT tag and count fix along with the rest of #297 (one folded tag per statement, real counts on every engine and protocol, transaction overlays, and the cluster fold). Closing this one; thanks for the groundwork.