fix: full-width planner with grid scrollbars inside the viewport

[aakvatech]

The planner previously inherited Desk's container width limit and had an unbounded grid with a 420px minimum height. Long task lists expanded the page, placing the horizontal scrollbar below the viewport and preventing a usable internal row scrollbar.

Scope width overrides to the Project Planner Desk page. Fill the available Desk content width, preserving the Dock and navigation. Measure the remaining viewport height below the real Desk header and update it on resize and page visibility/layout changes. Constrain the shell and let the grid own horizontal and vertical scrolling, with sticky column headers and keyboard focus. Controls and long feedback panels scroll separately and use at most 45% of the shell height so rows remain accessible.

Validation: all 7 UI tests pass, including viewport sizing, resize/page-show adjustment, and listener cleanup; production frontend build and diff checks pass. No backend behavior changed. Live Desk/browser layout has not been visually verified.

Deployment: rebuild frontend assets and reload Desk. Backport to version-16-hotfix.

[github-actions]

Backport failed for version-15, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin version-15
git worktree add -d .worktree/backport-43-to-version-15 origin/version-15
cd .worktree/backport-43-to-version-15
git switch --create backport-43-to-version-15
git cherry-pick -x 10430c0b23a9aa05e8df6f393d287b81153192f9

[github-actions]

Backport failed for version-15, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin version-15
git worktree add -d .worktree/backport-43-to-version-15 origin/version-15
cd .worktree/backport-43-to-version-15
git switch --create backport-43-to-version-15
git cherry-pick -x 10430c0b23a9aa05e8df6f393d287b81153192f9

[github-actions]

Successfully created backport PR for version-16-hotfix:

• [Backport version-16-hotfix] fix: full-width planner with grid scrollbars inside the viewport #44

[github-actions]

Successfully created backport PR for version-15:

• [Backport version-15] fix: full-width planner with grid scrollbars inside the viewport #48