Address inspector-peek review: stale docs + selection cleanup

Gadfly on #101:
- EditorRail's module doc still described a "fixed 20rem column / bottom
  sheet"; updated to the in-flow peek (desktop column, phone ≤50vh peek
  between canvas and mode bar).
- (correctness) A canvas-mode tap only deselected when railTab was
  'inspector', so a selection made, then routed through Journal/Assistant,
  survived a return to Fixtures/Plants — the canvas kept highlighting it
  with no inspector. Canvas modes now clear the selection unconditionally.
- Dedup: the "closing the inspector deselects" pair lived in both selectMode
  and the rail's onClose; extracted a clearSelection() helper (also used by
  exitFocus) and fixed the now-stale "leave an inspector alone" comment.

tsc + vitest + build green.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01H3zbym8Doka2d7D48maSgZ

web/src/editor/EditorRail.tsx

@@ -14,11 +14,14 @@ import { cn } from '@/lib/cn'
  *   - Selecting an object must land you in the inspector with no extra click.
  *     The editor watches the selection and switches to that tab itself, so the
  *     rail never becomes a thing you have to operate before you can edit.
- *   - The canvas has to stay worth watching while the agent edits it, so the
- *     rail is a fixed 20rem column and closes completely when nothing needs it.
+ *   - The canvas has to stay worth watching while the agent edits it, so the rail
+ *     closes completely when nothing needs it.
  *
- * On a phone the same tabs render in a bottom sheet, which is where the
- * inspector already lived.
+ * Layout differs by breakpoint. Desktop: a fixed 20rem column beside the canvas.
+ * Phone: an in-flow PEEK (#101) — a ≤50vh panel the editor's flex column places
+ * BETWEEN the canvas and the always-visible mode bar, so the canvas shrinks to
+ * keep the garden visible above it and the mode bar reachable below, rather than
+ * a bottom sheet that covered the whole garden.
  */
 
 export interface RailTab {