feat(control_plane): classify AggRole via real AggIntent, not a PromQL-string sniff

[zzylol]

Summary

derive_agg_role() used to guess a workload entry's AggRole (Quantile/Sum/Count/Topk/Other) by sniffing the leading token of its PromQL query_string — the same duplicate-classifier smell already retired from the live serving path (the old two-analyzer comparison in analyzer-parity-matrix.md, #422). Now parses the query through the same canonical pipeline capability_for()/serving uses (query_parser::parse_query_expr_canonical), runs it through the L3 rule-based optimizer (QueryOptimizer::new(0.0).optimize — TopKFusion is a pure structural rewrite, ignores the cost model, so the placeholder throughput doesn't affect the outcome) so topk(k, m) actually reaches an Aggregate{TopK} node instead of staying Sort+Limit, then classifies by the real outer AggIntent (collect_agg_intents, now pub(crate) for this reuse).

Two things this surfaced:

• (quantile_over_time(0.9, m[5m])) (redundant wrapping parens) — the old leading-token sniff finds an empty token at a ( and mis-defaults to Sum; real classification is unaffected by surface punctuation. New test pins this.
• topk_over_time(...) was in the old test's query list but isn't a real function this parser (or vanilla PromQL) recognizes at all — confirmed via grep, nowhere in query_parser/promql.rs or intent_algebra/lower.rs. A workload entry with that query_string would fail to parse anywhere else in the real pipeline too, so the old heuristic classifying it as Topk was itself the bug. Test updated to drop it, with an explanatory comment.

Test plan

• cargo build --workspace — clean, no new warnings
• cargo test --release --lib -p control_plane workload:: — 33/33 (32 existing + 1 new)
• cargo test --release --lib -p control_plane — 727/727 (one pre-existing, unrelated skip as before)

🤖 Generated with Claude Code

[zzylol]

Superseded by #429 (rebased onto main after #428 changed parse_query_expr_canonical's signature, plus a fix for the histogram_quantile classification fallout).