fix(relay): allow open relays to set their NIP-11 workspace icon (kind:9033) (#3998)

## Problem

The desktop deliberately shows the workspace icon editor on open relays
(#2640, gate: `canEditIcon` in
`desktop/src/features/communities/ui/EditCommunityDialog.tsx`) and
defers to the relay-side kind:9033 check — which required an admin/owner
row in `relay_members`. For a community with **no admin/owner row at
all** (the `ensure_configured_community` path, which never writes an
owner), every 9033 was refused and the icon was permanently unsettable.

**Correction from review (thanks @Dawn):** the original version of this
PR claimed nobody holds a role on an open relay. That's false —
`main.rs` bootstraps `RELAY_OWNER_PUBKEY` as owner regardless of
`BUZZ_REQUIRE_RELAY_MEMBERSHIP`, so a production open relay like
bb-block *does* have an owner row, and the old gate was refusing
everyone except that owner. The first revision of this diff would have
silently widened that owner-only control to any NIP-42-authenticated
sender.

## Fix — steward-wins

`may_set_workspace_profile(sender_role, membership_enforced,
community_has_steward)`:

| Relay mode | Community has admin/owner row? | Who may set the icon |
|---|---|---|
| Closed (`require_relay_membership=true`) | any | admin or owner
(unchanged) |
| Open | yes (e.g. bb-block) | admin or owner (unchanged posture) |
| Open | no (genuinely rosterless) | any NIP-42-authenticated sender |

- New DB helper `has_admin_or_owner(community)`
(`crates/buzz-db/src/relay_members.rs`); the call site only queries it
on open relays.
- The rosterless admit logs a `warn!` with the sender pubkey — 9033
writes no audit row and publishes no announcement event (unlike
9030/9031), so this is the only durable attribution.
- Kinds 9030–9032, NIP-42 auth, `AdminUsers` scope, ban gate, and icon
validation are all untouched.
- Doc comment fixed: cited nonexistent `canEditCommunityProfile`; real
symbol is `canEditIcon`.

## Test coverage — closing the mutation gap

Dawn's mutation testing showed the original unit tests pinned only the
helper's truth table: inverting the flag at the call site or deleting
the gate entirely survived the full suite.

- Unit tests now cover the 3-arg truth table (closed
steward-independent, open-with-steward stays steward-only,
rosterless-open admits).
- Two `#[ignore]`d Postgres integration tests drive
`handle_relay_admin_event` with a real `AppState` (open rosterless admit
→ steward appears → roleless refused again; closed relay member
refused). Wired into the Backend Integration CI job as a dedicated
nextest step.
- **Both of Dawn's mutants verified killed** at this head: flag
inversion fails 1 unit test; gate deletion fails both integration tests
(`Ok(())` where `Rejected` expected).

## CI wrinkle found and fixed: pre-existing schema drift

The first Backend Integration run of the new 9033 tests failed with
`column "icon" of relation "communities" does not exist` — migration
`0003_community_icon.sql` added the column, but `schema/schema.sql` (the
desired-state file that CI job applies via pgschema) was never updated.
Pre-existing drift, invisible until a test in that job actually wrote
the column. Fixed in `297148f62` (3-line addition to
`schema/schema.sql`).

## Receipts (at `1b4b52db8` code / `297148f62` head)

- `cargo test -p buzz-relay`: 835 pass, 1 fail —
`api::mesh_demo::tests::demo_join_forwarded_arm_round_trips_echo`,
pre-existing (fails identically at the old base and on clean main);
`telemetry::trace_context_lookup_does_not_enable_callsites` is a known
order-dependent flake, passes in isolation.
- `cargo test -p buzz-db`: 94 pass.
- Both ignored integration tests pass live against local Postgres.
- `cargo fmt --all -- --check`: clean.
- Live-local pass per TESTING.md at this head (release build, relay on
:3199, real WS + NIP-42 via nak):
- open rosterless: roleless key sets icon → NIP-11 serves it; `warn!`
with sender pubkey in the relay log
- open + owner row inserted: fresh roleless key refused ("must be admin
or owner"); owner sets icon
- closed relay (owner bootstrapped, `BUZZ_RELAY_PRIVATE_KEY` set): plain
member refused, owner sets icon, `javascript:` URL rejected, empty icon
clears (NIP-11 → null)

---------

Signed-off-by: npub1qyvc0c5kl4gqv2fd97fsk46tu378sqgy35vc83rvgfwne90sel7s0ed67d <011987e296fd5006292d2f930b574be47c7801048d1983c46c425d3c95f0cffd@buzz.block.builderlab.xyz>
Co-authored-by: npub1qyvc0c5kl4gqv2fd97fsk46tu378sqgy35vc83rvgfwne90sel7s0ed67d <011987e296fd5006292d2f930b574be47c7801048d1983c46c425d3c95f0cffd@buzz.block.builderlab.xyz>

schema/schema.sql

@@ -54,6 +54,9 @@ CREATE TABLE communities (
     id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
     host            VARCHAR(255) NOT NULL,
     signing_key     BYTEA,
+    -- Per-community workspace icon (NIP-11 `icon`), set via kind:9033.
+    -- Added by migration 0003; kept here so desired-state applies match.
+    icon            TEXT,
     created_at      TIMESTAMPTZ NOT NULL DEFAULT NOW(),
     archived_at     TIMESTAMPTZ,
     CONSTRAINT chk_communities_id_not_nil CHECK (id <> '00000000-0000-0000-0000-000000000000'::uuid)