Hide "Næsti hálfleikur" button after advancing to next half

[Copilot]

After clicking "Næsti hálfleikur", the button remained visible because timeElapsed was set to the half-stop time (e.g., 45 min), keeping the show condition !started && showInjuryTime && timeElapsed != 0 permanently true — making it easy to accidentally skip ahead multiple halves.

Root cause

pauseMatch(true) stored the absolute match clock position in timeElapsed, conflating "where is the clock display" with "how much has elapsed this half". The button visibility relied on timeElapsed != 0 as its signal, which was never reset.

Changes

• New halfOffset field on Match — stores the absolute start-of-half offset (e.g., 45 min at start of 2nd half). Parsed from Firebase with fallback to 0 for backward compatibility.
• pauseMatch(true) revised — sets halfOffset = halfStops[0] * 60 * 1000 and resets timeElapsed = 0, rather than accumulating into timeElapsed.
• Clock formula updated — milliSecondsElapsed = halfOffset + timeElapsed + (running ? serverTime - started : 0). Clock display is unchanged.
• isTimeNull updated — !started && !timeElapsed && !halfOffset so the clock still shows 45:00 at the start of 2nd half.
• Button condition tightened — "Næsti hálfleikur" now requires !!match.timeElapsed; countdown button requires !halfOffset in addition to !timeElapsed.

// Before: timeElapsed stayed at 45 min after click → button never hid
newState.timeElapsed = (newState.halfStops[0] ?? 0) * 60 * 1000;

// After: clock position split into offset + per-half elapsed
newState.halfOffset = (newState.halfStops[0] ?? 0) * 60 * 1000;
newState.timeElapsed = 0;  // button condition now false → hidden

Original prompt

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This section details on the original issue you should resolve

<issue_title>næsti hálfleikur</issue_title>
<issue_description>when clicking næsti hálfleikur it should be removed until we clicked again</issue_description>

<agent_instructions>basically if the current time is 0 (we have 2 notions of time, time elapsed and time set, on new half we set the time and set elapsed to 0, don't remember if these are the correct terms but thats how it works)</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes næsti hálfleikur #121

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