Consolidate CLI Opake construction onto a single builder
Two call sites built `Opake<ReqwestTransport, OsRng, FileStorage>`
with the same five-arg `Opake::for_account` + `OPAKE_INDEXER_URL`
env override: `CommandContext::opake` for user-facing commands and
`daemon::build_opake` for the daemon's per-task builder. When any
construction knob changed (the `now`/`now_micros` collapse; the
priority-chain cleanup's added `accountConfig` seed) both had to be
updated in parallel — bug-prone and nothing enforced the coupling.
Promote `build_opake(storage, did)` to `crate::session` as the one
construction path; `CommandContext::opake` forwards to it; daemon
imports it directly. Shape of the call sites is preserved, so no
behavior change.