PM-6309 Fix completed submission empty state and tab counts

[jmgasper]

Related JIRA Ticket:

https://topcoder.atlassian.net/browse/PM-6309

What's in this PR?

Registered members with no submissions now see Daniela's completed-challenge message, “Submission phase has ended,” without a Submit a solution button. The panel follows the Figma update, reusing the existing information icon and empty-state component while retaining the Review App handoff.

• Apply the ended state across challenge tracks and cancelled challenges. Offer upload only during open submission phases; keep neutral copy during registration and gaps between submission rounds.
• Hide zero or unavailable count badges on Registrants, Submissions, My Submissions, Forum, and review opportunity Applications tabs. Keep the tabs usable and continue displaying positive counts.
• Update the opportunities documentation and regression coverage, including deleting the last submission and returning its tab to a label without a count.

Validation

• yarn lint passes.
• NODE_OPTIONS=--max-old-space-size=12288 yarn run build passes with existing source-map, CSS-order, and bundle-size warnings.
• 136 tests pass across the challenge detail member flows, submission replacement, review details, challenge phase utilities, and challenge header suites. The local Jest command pins React and React DOM resolution to this worktree's dependencies because the shared installation otherwise resolves multiple React copies.
• Chromium checks of the rendered empty-state component and its real stylesheet pass at 1680px and 375px for both completed and active challenges, including icon size, spacing, centering, action visibility, and absence of horizontal overflow.