feat: pre-launch quick wins (COMMAND, HINCRBYFLOAT, Z*STORE, helm pvc, npm publish)

[kacy]

summary

pre-launch polish pass covering the most impactful gaps identified in the audit.

new commands

• COMMAND / COMMAND COUNT / COMMAND INFO / COMMAND DOCS — static metadata table for 150+ commands. this is what redis client libraries (jedis, lettuce, redis-py, ioredis) probe on connect to discover command metadata. without it those clients emit warnings or refuse to start.
• HINCRBYFLOAT — float increment on hash fields. rounds out the hash type alongside the existing HINCRBY.
• ZUNIONSTORE / ZINTERSTORE / ZDIFFSTORE — sorted set store variants. reuses the existing ZUNION/ZINTER/ZDIFF logic, writes result to dest key. dest and source keys must hash to the same shard (same constraint as the read-only variants).

helm

• added persistence section to values.yaml — off by default, enable with persistence.enabled=true and a PVC is created automatically
• new pvc.yaml template
• probes now use httpGet /health when metricsPort is configured (was bare tcpSocket before)
• emptyDir fallback includes a prominent WARNING comment so nobody silently loses data in production

docs

• readme: docker one-liner quickstart so people can try ember in seconds without installing anything
• compatibility.md: all new commands marked ✓; MULTI/EXEC section expanded with cross-shard atomicity caveat and hash tag example
• updated feature list to reflect HINCRBYFLOAT, ZUNIONSTORE/ZINTERSTORE/ZDIFFSTORE, COMMAND introspection

ci

• release workflow: new npm job publishes ember-ts to npm on every tagged release
  • requires NPM_TOKEN secret in repo settings

what was tested

• cargo check -p emberkv-core -p ember-protocol -p ember-server clean on both agents
• COMMAND introspection: verified static table covers all 150+ commands with correct arity/flags
• ZUNIONSTORE/ZINTERSTORE/ZDIFFSTORE: same routing + AOF pattern as existing ZUNION/ZINTER/ZDIFF
• HINCRBYFLOAT: AOF records result string (not delta) — avoids float rounding drift on replay, consistent with INCRBYFLOAT
• helm: helm template passes; probes render correctly with and without metricsPort

design notes

the COMMAND table is a static OnceLock<Vec<CommandEntry>> initialized at first call — no heap allocation on the hot path. COMMAND INFO name [name ...] returns nil for unknown commands (matching redis behavior). COMMAND DOCS returns an empty map — sufficient for client compat, avoids the maintenance burden of full docs inline.

ZUNIONSTORE/ZINTERSTORE/ZDIFFSTORE route to the dest key's shard. all source keys must share that shard (enforced with a MOVED error if not). this is the same constraint as RENAME and the existing cross-shard store ops.