feat(send): delivery-window + persistence axes — CLI flags + spool schema (v0.15.0 W2)

ADR-0028 W2 (doyle-ratified drain-surface split + deferred-mirror). Expose the
delivery-WINDOW axis on `spt send` and tag it onto the spool so the right drain
surface picks each row up. The broker / EndpointInputReq is untouched — the
window is a caller-side spool tag, orthogonal to the send-time `.idle`
inject-vs-spool gate (Q3: broker-inject-at-send-time stays the sole idle gate).

CLI (`spt send`):
- `--idle-only` / `--active-only` — mutually exclusive delivery-window group.
  `--active-only` RENAMES `--deferred` (pure rename; the internal `deferred=1`
  column + `api poll --include-deferred` keep their names). default = both windows.
- `--ephemeral` — persistence axis; the flag + column land now (stored), the
  evaporation trigger wires in W3 alongside the channel axis (force-native +
  ephemeral is the concrete no-carrier-at-window case).
- cmd_send maps the flag → window and spools via deliver::send_windowed; the
  broker's active/idle hint is superseded by the explicit window.

Spool schema (additive, mirrors how `deferred` was added):
- New columns `"window"` (default|idle_only|active_only), `channel`
  (any; prefer/force_native wire in W3), `ephemeral`. `"window"` is double-quoted
  in all SQL (SQLite keyword).
- `deferred` is RETAINED as a back-compat MIRROR — derived from `window` at the
  SINGLE insert chokepoint (deferred=1 IFF window='active_only'), so the ~40
  deferred-keyed reads stay correct at zero churn. A unit test pins the invariant
  across all three window values.

Drain-surface split (Q1 — only the ACTIVE-hook side re-points):
- New `drain_active_window_at(perch, include_deferred)`: include_deferred ?
  window != 'idle_only' ({default,active_only}) : window = 'default'. Re-points
  poll_drain (api poll) + cmd_worker_poll — both now SUPPRESS idle_only (it
  reaches the receiver only via the idle/wake relay). The resting-gate narrowing
  (REQ-INST-6) flows through unchanged.
- The idle/wake side is UNCHANGED: deferred=0 already == {default, idle_only} ==
  the relay/idle-drain target set, so the relay (ready.rs) + the idle-transition
  drain need no edit. No second drain fn.

deliver::send_windowed: active_only = spool-only (no live wake); default/idle_only
try a live TCP handoff first (the relay IS the idle wake), then spool tagged with
the window. send / send_deferred are untouched (other callers).

Tests: spool deferred-mirror invariant (3 windows) + active-window idle_only-
suppression/include_deferred; delivery poll_drain suppresses idle_only while it
reaches the relay; CLI parse for --active-only/--idle-only/--ephemeral +
mutually-exclusive group. Full nextest -p spt-daemon (483) + -p spt (292) green;
clippy --workspace 0; traceable EXIT0; xtask gen+check OK (reference.md regen for
the new flags, no internal codes).

[impl->REQ-MSG-DELIVERY-AXES]

Co-authored by: todlando
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015e2dT1NAirnsahCJs4BX3Y