…fied aggregates

Second mechanism of #1196, exposed by the reporter's v0.10.6 retest: every
relationship-expansion site capped its output buffer at bind_cap*10, so edges
past the cap were silently dropped BEFORE WHERE and aggregation ever ran.
count() then reported the scanned prefix as if it were a fact — 9,360 of
13,691 DEFINES field-measured at --max-rows 1000 — and a LABEL on the source
did not protect you (the label workaround only ever fixed source
enumeration, which #1323 already made exact). max_rows is an output-row
limit per the public header; projection already enforces it.

All five capped sites now share one growable append (geometric growth,
size_t sizing): the per-hop expansion, its fixed/variable-length helpers and
process_edges, the bound-terminal driver, and the cross-join outer buffer.
Only allocation failure stops materialisation; match_count stays truthful
either way, so the #627 OPTIONAL contracts hold (a saturated buffer can no
longer exist, and the fallback rows share the same append). The #601
deadline still bounds pathological time, and hop caps keep bounding depth —
this removes only the silent row-dropping.

Regression test: 2 labeled sources x 30 edges with max_rows=2 — the old cap
returned count=20; ground truth 60 now holds, and the list form returns
exactly max_rows rows. Proven RED before and RED again on revert; cypher
181/181 and mcp suites green, including every OPTIONAL/#627 semantics test.

Fixes #1196 (together with #1323, which fixed the unlabeled source scan).

Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>