* fix(relayer): hash categories with keccak256 like the SDK

msgboardContentSource used stringToHex(..., { size: 32 }) for plain
category names, which diverged from MsgBoardClient.doPoW / categoryHash
(keccak256). Watchers and publishers of the same label could miss each
other.

Use categoryHash from @msgboard/sdk; keep 0x bytes32 passthrough so
callers that pre-hash (e.g. Valaxy) stay correct. Bump to 0.5.0.

* chore(relayer): bump workspace dependents and lockfile to 0.5.0

Keep monorepo package.json ranges and package-lock in sync after the
@msgboard/relayer 0.5.0 bump so npm ci succeeds in CI.

* docs: align waku/sponsor category notes with relayer keccak default

toCategoryHex now matches SDK categoryHash (keccak). Update waku-relay
docs/tests that still claimed ascii32 was the relayer convention, and
clarify sponsor spam still opts into legacy pad on purpose.

* fix(relayer): keep plaintext categories as UTF-8 zero-pad

Product intent: a category may be encoded letters (zero-padded bytes32).
Do not force keccak256 on every plaintext string.

toCategoryHex now:
- plain string → stringToHex(..., { size: 32 })
- 0x + 32-byte hex → passthrough (SDK categoryHash / Valaxy)

Drop the 0.5.0 breaking bump; ship as 0.4.1 with explicit passthrough
docs. Align waku/sponsor notes with the pad default.