Dashboard tile head: collapse the action icons into a ⋯ menu, consistent across every style

[BorisTyshkevich]

Problem

PR #538 (#535) added duplicate, widen and expand to a Dashboard panel tile's
head. Together with the drag grip and the delete button that were already there,
the head now carries five controls sharing one flex row with the tile title —
and every action is flex-shrink: 0, so the title ellipsizes away first. On a
tile a single grid column wide (≈93px at twelve columns) there is no row left to
compete for.

A second, independent problem: the action set is not consistent between
Dashboard styles. Delete is gated twice to the grafana-grid engine — a CSS
ancestor scope (.dash-gg-grid .dash-gg-tile:hover .dash-gg-del) and an
activeEngine === 'grafana-grid' check inside its own click handler — so
Report, 2 columns and 3 columns have no delete at all, and a flow KPI band
member has neither delete nor widen under any style.

Behaviour

Mode	Head
Edit	grip · title · widen · ⋯
View	unchanged — the single direct expand icon, no menu

The ⋯ menu always lists all four actions, in the design's order, with remove
last behind a separator: Duplicate panel, Widen (carrying widenLabel's
dynamic destination text), Open in Workbench and run, Remove tile. A row
that cannot run is listed and disabled with a sentence saying why — a menu whose
vocabulary changed with the layout style would teach the user nothing, and the row
is itself the place to explain. This reverses #535's "nothing to open means no
control, not a disabled one" for the menu only; the inline widen keeps that rule,
because a bare icon has only a tooltip.

Widen keeps an inline button as well: it is the one size adjustment users make
constantly (#535), and it is the one a narrow tile can withdraw. A CSS container
query on the tile head hides it below ~236px of head content box (≈260px of tile),
where the ellipsized title has nothing left to give. Its menu row stays, so widen
is never unreachable.

Remove becomes engine-independent by construction. It also absorbs #537 — see
below — because shipping delete into three more styles while it orphaned a query
would multiply that bug's blast radius.

Scope notes

• Closes Tile-header delete should remove the panel’s owned query atomically #537. The tile-header trash dispatched the document-only
  remove-tile command, which leaves workspace.queries untouched. Since Separate Library queries from dashboard-owned query copies #427
  makes every panel tile the sole owner of a saved-query copy, that left the copy
  with zero owners — which is exactly what makes a query a Library query — so a
  deleted panel reappeared as an apparently standalone Library entry. It now uses
  the same confirmed, ownership-proven, two-resource path the Dashboards tree
  does, and fails closed for a missing, shared, ambiguous, retargeted or non-panel
  query.
• Partly reverses Dashboard tree: replace overflow menus with direct Panel focus, edit and delete actions (#429 phase 4) #494 for one surface. Dashboard tree: replace overflow menus with direct Panel focus, edit and delete actions (#429 phase 4) #494 removed the ⋯ from every
  Dashboards-tree row on the grounds that nothing a row can do should hide behind
  a second press. That holds for rows — two controls in a fixed-width side pane —
  and is not reopened; a tile head is a different surface. Recorded in the ADR-0003
  addendum, CHANGELOG.md, and roadmap Roadmap to 1.0.0 #68.
• Supersedes Dashboard tile removal leaves saved-query star state inconsistent #370's tile-removal semantics for panel-owned queries (the
  membership normalisation and spec.favorite mirroring it defined are unchanged;
  they run inside the atomic transform).
• Known costs, filed rather than fixed: A tile whose owned query is missing or shared cannot be removed from any surface #542 (a tile whose query is missing or
  shared is now unremovable from any surface — Tile-header delete should remove the panel’s owned query atomically #537 requires fail-closed) and
  A two-resource write (duplicate / remove panel) silently drops Full view #543 (a two-resource write drops the transient Full view, pre-existing since
  feat(#535): duplicate, widen and expand actions on a panel tile head #538's duplicate).

Acceptance

• Edit head is grip → title → widen → ⋯; View head unchanged.
• The menu lists all four actions always, with reasons on unavailable rows,
  and remove separated and last.
• Remove works under all five styles and on a flow KPI band member, atomically
  with the panel's owned query, behind a confirmation, failing closed.
• The inline widen withdraws on a narrow tile via a container query, with the
  menu row remaining; proven in a real browser.
• The ⋯ stays visible for its own menu's lifetime (aria-expanded), and the
  menu does not overflow the viewport's right edge.
• npm test green with the per-file coverage floors; e2e on all three engines.

[BorisTyshkevich]

closed by #545