refactor: name stock demo keyspaces after the mode

[Code0987]

Why

Stock -demo-keyspace names were themed (tags, board, profile, doc, flags, embeddings). Operators had to remember a nickname per type.

What landed

One rule: name = lowercase Mode.String().

Mode	Keyspace
CacheOnly	cacheonly (sc / scbench default)
Set	set
ZSet	zset
Hash	hash
JSON	json
Bitmap	bitmap
VectorSet	vectorset

Node registration, sc/scbench defaults, cluster3, and product/example docs that talk to the stock node. In-process examples that register their own names (billboard tags, hash demo profile) are unchanged.

Tests

go test ./cmd/sc ./cmd/scbench ./examples/vecset ./examples/hash ./examples/json ./examples/bitmap

Bench risk

None. Demo keyspace names and docs only.

[github-actions]

SuperCache bench vs main

Both sides ran once on this same GitHub runner (main, then this PR). Not a merge gate.

Baseline: b2f2c65 (2026-09-06T12:18:54Z) → this run: b2f2c65 (2026-09-06T12:18:07Z)

scbench smoke

cell	ops/s (main → PR)	Δ ops/s	p50	p99
get/hit n=1 c=1 uniform	8711 → 8748	+0.4%	114µs → 114µs	194µs → 196µs
get/hit n=1 c=10 uniform	34614 → 34049	-1.6%	263µs → 267µs	781µs → 802µs
get/hit n=3 c=10 uniform	39420 → 38373	-2.7%	222µs → 228µs	856µs → 909µs
miss/miss-cacheonly n=1 c=1 uniform	8582 → 8853	+3.2%	115µs → 112µs	218µs → 197µs
miss/miss-cacheonly n=1 c=10 uniform	34990 → 36297	+3.7%	258µs → 251µs	831µs → 780µs
set/put n=1 c=1 uniform	8448 → 8411	-0.4%	117µs → 116µs	207µs → 211µs
set/put n=1 c=10 uniform	32827 → 33032	+0.6%	279µs → 277µs	822µs → 812µs

Δ ops/s: green-ish is higher throughput. Latency: lower is better.

go test -bench (ns/op)

benchmark	ns/op (main → PR)	Δ	allocs/op
BenchmarkEngineDelete	887 → 841	-5.2%	6 → 6
BenchmarkEngineGetHit	1192 → 1189	-0.3%	15 → 15
BenchmarkEngineGetHitParallel	1217 → 1231	+1.2%	15 → 15
BenchmarkEngineGetMissCacheOnly	854 → 869	+1.8%	14 → 14
BenchmarkEngineGetMissCacheOnlyParallel	681 → 666	-2.2%	14 → 14
BenchmarkEngineGetMissLoadThrough	1663 → 1630	-2.0%	24 → 24
BenchmarkEngineGetMissLoadThroughParallel	1800 → 1825	+1.4%	23 → 23
BenchmarkEnginePut	1615 → 1622	+0.4%	18 → 18
BenchmarkEnginePutParallel	1434 → 1422	-0.8%	18 → 18
BenchmarkStoreBitSet	112 → 112	+0.1%	1 → 1
BenchmarkStoreCGetHit	72 → 74	+2.3%	0 → 0
BenchmarkStoreCIncr	101 → 101	-0.2%	1 → 1
BenchmarkStoreCMSIncr	121 → 121	+0.2%	0 → 0
BenchmarkStoreCMSIncrN	121 → 121	+0.2%	0 → 0
BenchmarkStoreGeoAdd	9567 → 9996	+4.5%	2 → 2
BenchmarkStoreGeoPosHit	88 → 88	-0.3%	0 → 0
BenchmarkStoreGeoPosMiss	87 → 87	+0.1%	0 → 0
BenchmarkStoreGetHit	293 → 294	+0.2%	2 → 2
BenchmarkStoreGetHitParallel	336 → 351	+4.6%	2 → 2
BenchmarkStoreHGetHit	91 → 91	-0.0%	1 → 1
BenchmarkStoreHGetMiss	85 → 85	-0.2%	0 → 0
BenchmarkStoreHLLAdd	100 → 100	+0.1%	0 → 0
BenchmarkStoreHSet	10648 → 10698	+0.5%	3 → 3
BenchmarkStoreJsonSet	26485 → 26340	-0.5%	207 → 207
BenchmarkStorePut	301 → 301	-0.2%	2 → 2
BenchmarkStorePutParallel	343 → 342	-0.2%	2 → 2
BenchmarkStoreSetAdd	9230 → 9230	+0.0%	2 → 2
BenchmarkStoreSetContainsHit	86 → 87	+1.9%	0 → 0
BenchmarkStoreSetContainsMiss	84 → 84	+0.6%	0 → 0
BenchmarkStoreTopKAdd	987 → 982	-0.5%	20 → 20
BenchmarkStoreVAdd	107236 → 107743	+0.5%	511 → 513
BenchmarkStoreVSim	90283 → 89464	-0.9%	530 → 530
BenchmarkStoreZAdd	9566 → 9935	+3.9%	2 → 2
BenchmarkStoreZScoreHit	86 → 86	+0.1%	0 → 0
BenchmarkStoreZScoreMiss	86 → 86	+0.2%	0 → 0

_{Posted by CI bench job. Not a merge gate.}