feat(scene): restructure to the v1 single-column TUI layout

[esengine]

The user supplied a new design mock (`reasonix-v1`) that's a complete
shape change from the desktop-style mock we'd been targeting:

• Single-column terminal stream (cards + boot block), no permanent
  sidebar / context pane.
• Fixed bottom dock: composer input row → meta row (kbd shortcuts)
  → status bar (multi-segment).
• Each card identified by a colored prefix glyph + label, no
  enclosing boxes. The mock's CSS explicitly states the design
  rule: "NO enclosing boxes, every block uses a left-rail."

This PR replaces `buildTraceFrame` end-to-end to match, supersedes
#1007 which was building on the old desktop shape.

Layout

Outer column (background bg):

• scroll area (`height: fill`): boot block when no cards, otherwise
  one row per card with kind-colored glyph + label + summary.
• dock (intrinsic height): composer row → meta row → status bar.
  Approval, slash overlay, and sessions picker fold in above the
  composer row when active.

Three-pane sidebar/ctxpane code is gone — was the wrong shape for
the v1 mock. The "MISSION CONTROL" right rail in the mock is a
toggleable secondary view; we'll wire it as an opt-in render mode
later, not as the default layout.

Palette swap

`src/cli/ui/scene/theme.ts` switched from the desktop oklch tokens
to the v1 set:

```
bg #0f1018 bg2 #161824
fg #e8e9f3 fg1 #a8aabd fg2 #6b6e85 fg3 #3d4055
ds #6b85ff dsBright #8b9fff dsPurple #a78bfa
ok #5eead4 warn #fbbf24 err #fb7185 info #60a5fa
```

Single source of truth — every styled run reads from PALETTE.

Specific row shapes

• Boot block (empty state): `● REASONIX DeepSeek code agent` banner,
  then `model` / `cwd` / `mcp` rows, then a hint line with
  kbd-colored glyphs for `/` `@` `!`.
• Card row: `
  ` per kind — YOU (blue),
  THINKING (purple), reasonix streaming (teal), tool (muted), diff
  (purple), error (err), warn (warn).
• Composer row: `❯ ▮ ` on a bg2-tinted line, fixed
  height 1.
• Meta row: left (`↵ send · ⇧↵ newline · / cmd · @ file · ! shell`),
  spacer, right (`esc cancel · ↑ history`). Each kbd glyph in ds
  blue, label in fg2 muted — matches the mock's hint row.
• Status bar: `● reasonix · model X · mode review · busy/idle` on
  the left; spacer; `wallet ¥X · cwd ~/path` on the right.

What still falls short of v1

• No ASCII REASONIX banner art (the 6-row block-letter logo). Too
  big for 80-col terminals; the compact `● REASONIX …` banner
  ships instead. Wide-terminal variant is a follow-up.
• Card head/body separation — each card is still one summary line.
  Multi-line bodies (THINKING italic body, diff hunks, bash output)
  need richer payloads in `SceneTraceCard`. Separate PR.
• Status bar ctx / tokens / cost / turn / git segments — need
  telemetry + git status wiring not yet exposed to scene.
• MISSION CONTROL right rail — separate toggleable view.

Tests

`tests/scene-trace-frame.test.ts` rewritten end-to-end against the
new structure (38 cases, all green). Shape queries use
`scrollOf` / `dockOf` / `composerRowOf` / `statusRowOf` /
`metaRowOf` helpers instead of fixed indices, so future row
reorderings don't churn the file.

`RESERVED_ROWS` (used by `cardsForHeight`) bumped 3 → 4 — composer

• meta + status = 3 rows; boot block adds 1 more on cold-start.

`npm run verify` green via prepush gate.

Refs #868