docs(v0.1-tech): switch Wi-Fi to on-demand model, off by default

Always-on station mode burns ~410 mAh/day on the radio alone; on-demand
drops that to ~25 mAh/day at 10 Publishes/day. Radio comes up on Ctrl-G
with a 10 s association timeout, holds for a ~90 s grace window after
each Publish, then tears down. SNTP cached up to 24 h to avoid
re-querying every Publish.

Also removes stale SoftAP provisioning bullets that contradicted the
"v0.1 has no provisioning module" stance later in the same doc.

docs/v0.1-mvp-technical.md

@@ -45,7 +45,7 @@ blocked by I/O.
 | Task          | Core | Stack | Responsibility                                           |
 | ------------- | ---- | ----- | -------------------------------------------------------- |
 | `usb_task`    | 0    | 8 KB  | TinyUSB host loop, decode HID reports, post `KeyEvent`s  |
-| `wifi_task`   | 0    | 8 KB  | Station mode only (no provisioning AP); expose status    |
+| `wifi_task`   | 0    | 8 KB  | On-demand station: off by default, brought up by `Ctrl-G` |
 | `ui_task`     | 1    | 16 KB | Consume `KeyEvent`s, mutate editor state, enqueue render |
 | `render_task` | 1    | 12 KB | Drain render queue, do partial/full refresh on EPD       |
 | `git_task`    | 1    | 32 KB | Triggered by `Ctrl-G`; runs gitoxide commit + push       |
@@ -67,7 +67,7 @@ read snapshot (render diff).
    └─ present → continue
 5. Init SPI bus (shared: EPD + SD on different CS)
 6. Init EPD, full refresh: splash + boot log
-7. Start tasks: usb, wifi (station), ui, render
+7. Start tasks: usb, wifi (spawned in `Off` state — no radio bring-up), ui, render
 8. ui_task opens /sd/repo/notes.md, places cursor, enqueues full render
 9. STEADY STATE
 ```
@@ -156,15 +156,32 @@ Storage split rationale:
 - The file is read fully into the rope at boot. v0.1 caps file size at
   256 KB; larger files refuse to open with a clear message.
 
-### `wifi` — provisioning + station
+### `wifi` — on-demand station
 
-- Provisioning: SoftAP `typewriter-setup`, captive-portal DNS, tiny HTTP
-  server (`esp-idf-svc::http`). Form submits config; on success, restart in
-  station mode.
-- Station: reconnect with exponential backoff (1, 2, 5, 10, 30, 60 s, hold
-  at 60). Status exposed via a `WifiState` atomic enum.
-- Time sync via SNTP — needed for commit timestamps. Failure is logged but
-  non-fatal; commits use device uptime if SNTP fails.
+- **Off by default.** The radio is powered down (`esp_wifi_stop`) except
+  during a Publish and a short grace window after. This is the load-bearing
+  battery decision: always-on station mode burns ~410 mAh/day just for the
+  radio; on-demand is closer to ~25 mAh/day at 10 Publishes/day. See
+  [qfd.md H13](qfd.md#6-critical-performance-budget).
+- **Bring-up on `Ctrl-G`.** `wifi_task` transitions `Off → Associating →
+  Connected`. Association timeout: 10 s. If association fails, the local
+  commit is preserved and the status line shows `⌁ ✗`; no background retry.
+- **Grace window** of ~90 s after a Publish completes. A `Ctrl-G` inside
+  the window reuses the connection (no second association cost). If no
+  Publish fires before the window expires, the radio tears down.
+- **No reconnect-backoff state machine.** There is nothing to reconnect to
+  when the user isn't trying to Publish. Single-shot try-on-demand replaces
+  the exponential-backoff approach.
+- **SNTP** runs on the first successful bring-up of a power session. The
+  result is cached for up to 24 h; subsequent Publishes use the cached time
+  for the commit message. Falls back to device uptime if SNTP has never
+  succeeded — logged but non-fatal.
+- **Status exposed via a `WifiState` atomic enum** (`Off`, `Associating`,
+  `Connected`, `Failed`).
+
+On-device provisioning (SSID, PAT rotation, etc.) is deliberately deferred
+to v0.9. v0.1 reads all config from the binary at build time — see
+"Provisioning — build-time only" below.
 
 ### `git` — commit + push