Tighten indexer URL priority chain
The `resolve_indexer_url` chain had four levels with priority 3 dead
and priority 2 inert on cold start:
1. Runtime override — `set_indexer_url()`
2. PDS accountConfig — mirrored from `accountConfig.indexerUrl`
3. Caller-provided `default: Option<&str>` (always None)
4. Compile-time `DEFAULT_INDEXER_URL`
Priority 3 was self-labeled "legacy arg, usually None"; every Rust
caller passed None and the SDK TS wrappers literally passed `null`
through to the WASM. Priority 2 was populated only by
`set_account_config`, so on cold start it was always empty — the
effective chain collapsed to "runtime override || compile-time
default," with the user's PDS-configured URL never consulted.
Collapse to three real levels:
1. Runtime override — unchanged.
2. PDS accountConfig — now seeded best-effort in `for_account`
via `get_account_config().await`, so the chain actually works
on a fresh boot. Offline, missing record, or auth blips fall
through silently to the compile-time default.
3. Compile-time default — unchanged.
Side effects of the collapse:
- `resolve_indexer_url` returns `String` rather than
`Result<String, Error>`. The `NotFound` arm was unreachable
under the old chain too (the const fallback is non-empty);
the signature now tells the truth.
- The `default: Option<&str>` parameter is removed from
`resolve_indexer_url` and from `request_sse_token`, `list_inbox`,
`list_workspace_documents`, `discover_member_keyrings`.
- The five WASM bindings mirroring those methods
(`listWorkspaces`, `listInbox`, `listWorkspaceDocuments`,
`discoverMemberKeyrings`, `requestSseToken`) stop taking the
`Option<String>` argument — matching what the SDK TS wrappers
already did internally.
- `startSseConsumer(indexerUrl)` keeps its JS-side parameter but
its semantics are upgraded: a caller-supplied URL is promoted to
the runtime override (priority 1) via `set_indexer_url` before
resolving, so it wins over PDS config and persists across
subsequent indexer calls on the same Opake. A dropped URL
landing on the old priority 3 would have lost to the PDS config
— this is arguably a bugfix.
- The CLI `--indexer` flag on `opake inbox` now promotes via
`set_indexer_url` rather than passing through a dead parameter,
matching the same runtime-override semantics.