docs: drawer surface_validate + sorting + job states

Documents the drawer enhancements landed across 1.0.0-44 → 1.0.0-51:

- Job states section explains passed / failed / cancelled / unknown,
  including when 'unknown' fires (stuck-job timeout OR container
  restart cancelling the asyncio task).
- Drive drawer section covers the new surface_validate visualization:
  vital-signs strip (Start / Elapsed / ETA / Finish / Temp), four
  per-pattern meters with split write/verify halves, phase caption,
  completed-pattern duration history.
- Failure reason block describes the three-tier source resolution
  (stage error_text → job error_text → heuristic) and what shows up
  when none is available.
- Column sorting describes the click-to-cycle behaviour and the
  localStorage persistence that survives SSE refreshes.

Plus an explicit warning: don't `--build` while burn-ins are running
(now classified `unknown` instead of `failed` — but still better to
avoid the kill in the first place).

README.md

@@ -106,6 +106,91 @@ Click the red ✕ next to a running job. The orchestrator:
 Cancellations are durable — restart the container and queued jobs resume,
 cancelled jobs stay cancelled.
 
+### Job states explained
+
+| State       | When it's set                                                                 |
+|-------------|-------------------------------------------------------------------------------|
+| `queued`    | Submitted, waiting for a `max_parallel_burnins` slot                          |
+| `running`   | Actively executing some stage                                                 |
+| `passed`    | All stages finished green                                                     |
+| `failed`    | A stage failed deterministically (bad blocks > threshold, SMART failure, etc.) |
+| `cancelled` | Operator clicked ✕                                                            |
+| `unknown`   | Job was alive but its outcome is indeterminate — see below                    |
+
+`unknown` fires in two situations:
+
+1. The stuck-job detector (`stuck_job_hours`, default 7 days) trips because
+   the job has been running too long without finishing.
+2. The asyncio task got cancelled mid-stage by something *other* than an
+   operator click — usually a container restart (`docker compose up -d`,
+   `--build`, or the host rebooting). Burn-in source code goes through
+   the Dockerfile `COPY`, so any source-code deploy recreates the
+   container, drops the SSH connection to TrueNAS, and would orphan the
+   running burn-in. Avoid `--build` while burn-ins are active.
+
+When `unknown` fires the drawer's per-stage Reason block shows
+*"Task cancelled mid-run — likely container restart or shutdown"* so the
+classification is explicit, not silent.
+
+---
+
+## Drive drawer
+
+Click any drive row to slide a detail drawer down from the top. Three tabs:
+
+- **Burn-In** — per-stage breakdown of the latest job
+- **SMART** — short/long test states + cached SMART attributes
+- **Events** — last 50 audit events for the drive
+
+### Surface-validate visualization
+
+For drives in a `surface_validate` stage (running or finished), the Burn-In
+tab renders:
+
+1. **Vital-signs strip** — `Start` (with date) · `Elapsed` · `ETA` (duration
+   remaining) · `Finish` (wall-clock estimate, browser-local timezone) ·
+   `Temp` (cool/warm/hot colour). Computed from data in the drawer payload;
+   ETA + Finish suppressed below 0.5% so you don't see a "Finish: Jun 22"
+   stutter at the very start.
+2. **Four pattern meters** — `0xaa` / `0x55` / `0xff` / `0x00`. Each meter
+   is split into a left half (write phase, blue) and a right half (verify
+   phase, green). Current pattern's label glows blue; completed patterns'
+   labels go green. This translates badblocks's per-phase percent into
+   monotonic 0-99% overall progress, so the bar never appears to "rewind"
+   when a new phase starts.
+3. **Phase caption** — explicit text: *"Pattern 2 of 4 · Verify 0x55 · 47%
+   within phase"*. Makes the visual grammar unambiguous.
+4. **Completed-pattern history** — once pattern 1 finishes, a chip appears
+   showing `0xaa: 14h 22m`. Lets you predict the rest of the run from the
+   first pattern's elapsed time.
+
+### Failure reason block
+
+Stages that ended `failed` / `cancelled` / `unknown` show a coloured Reason
+pill at the top of the stage section. Sources, in order of preference:
+
+1. The stage's own `error_text`
+2. The parent job's `error_text` (backfilled by the drawer when the stage's
+   own is empty — catches orphan rows from hard crashes)
+3. A heuristic: if the log is tiny and no real progress was recorded,
+   *"Stopped without recording an error — likely cause: SSH connection drop
+   or container restart while this stage was running"*
+
+Otherwise: *"No error message recorded."* — there's never a blank where you
+expect to see why something broke.
+
+### Column sorting
+
+Click any column header (Drive, Serial, Size, Temp, Health, Short SMART,
+Long SMART, Burn-In) to sort. Cycle: ascending → descending → cleared. Sort
+state persists in `localStorage` so it survives page reload AND every
+SSE-driven tbody refresh (~12 s poll cycle). Empty values always sink to
+the bottom regardless of direction.
+
+Sortable values are emitted as `data-sort-*` attributes on each `<tr>`,
+with numeric priority maps for SMART states (e.g. `running` always sorts
+ahead of `idle`).
+
 ---
 
 ## Drive locks