feat: Display and edit dates in the browser's local time zone

[dblythy]

Issue

Closes #482

Approach

Adds a per-app useLocalTime config flag. When enabled, dates in the data browser (and other date displays) are shown and edited in the viewer's browser time zone instead of UTC. Dates are always stored in UTC; editing is WYSIWYG, so the local wall-clock you type or pick is converted to UTC on save. The default is unchanged (UTC).

This generalizes the existing binary local/UTC handling (already used for Push scheduling) via dateStringUTC(date, useLocalTime) plus shared dateInputString/parseDateInput helpers in lib/DateUtils, with no new dependency.

• Scope: data browser (display, inline edit, edit-row dialog, date filter), plus job status/scheduling, config history, and cert/key expiry displays.
• Out of scope: Push scheduling (keeps its own local_time toggle) and the Analytics chart's separate date handling.
• Supersedes the display-only POC Timezone configuration #914, which was closed in 2016 before this was a wanted feature.

Display: same rows and server, viewed as UTC vs local

Test browser zone: Australia/Sydney (GMT+11 AEDT / GMT+10 AEST). 13:45:30 UTC → 0:45:30 GMT+11 (day rolls over); 21:00 UTC → 7:00 GMT+10; DST is resolved per date.

useLocalTime unset (UTC, unchanged)	useLocalTime: true (browser local)

Editing is WYSIWYG: edit in local, store in UTC

Editing the Morning row in the local app. The inline editor shows the local wall-clock (2020-01-16T00:45:30), changed here to 09:00:

Committed, so the cell shows 16 Jan 2020, 9:00:00 GMT+11:

Stored as UTC (the same instant): the UTC app shows 15 Jan 2020, 22:00:00 UTC (raw REST value 2020-01-15T22:00:00.000Z). In the UTC app, typed input without a Z is still interpreted as UTC, so the default behavior is unchanged.

Tasks

• Add tests
• Add changes to documentation (guides, repository pages, in-code descriptions)

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📥 Commits

Reviewing files that changed from the base of the PR and between 9db24be and bb1757f.

📒 Files selected for processing (20)

• README.md
• src/components/BrowserCell/BrowserCell.react.js
• src/components/BrowserFilter/BrowserFilter.react.js
• src/components/BrowserFilter/FilterRow.react.js
• src/components/DateTimeEditor/DateTimeEditor.react.js
• src/components/DateTimeEntry/DateTimeEntry.react.js
• src/components/PushCerts/CertsTable.react.js
• src/dashboard/Account/AccountOverview.react.js
• src/dashboard/Data/Browser/BrowserTable.react.js
• src/dashboard/Data/Browser/DataBrowser.react.js
• src/dashboard/Data/Browser/EditRowDialog.react.js
• src/dashboard/Data/Browser/Editor.react.js
• src/dashboard/Data/Config/ConfigDialog.react.js
• src/dashboard/Data/Jobs/Jobs.react.js
• src/dashboard/Data/Jobs/JobsForm.react.js
• src/dashboard/Settings/AppleCerts.react.js
• src/lib/DateUtils.js
• src/lib/ParseApp.js
• src/lib/tests/DateUtils.test.js
• testing/preprocessor.js

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