Add moon-area bilingual datetime and lunar hour display

[Heersin]

Motivation

• Add a two-line datetime under the moon to show an English Gregorian date/time and a Chinese lunar date with 时辰, and visually align the bottom of that block with the intro copy baseline as requested.

Description

• Inserted a moon-datetime container with two lines in layouts/index.html and set aria-live="polite" for dynamic updates.
• Extended assets/js/moon-phase.js to keep the moon-phase logic and also populate the first line with Gregorian datetime using Intl.DateTimeFormat('en-US') (24h with seconds) and the second line with lunar month/day using Intl.DateTimeFormat('zh-CN-u-ca-chinese') plus the computed earthly-branch hour (时辰).
• Adjusted assets/css/main.css by converting .moon-wrap to a column flex layout and adding .moon-datetime / .moon-datetime-line styles so the two-line block sits at the bottom of the moon column and matches the visual alignment.
• Preserved existing moon phase rendering and accessibility label behavior.

Testing

• Ran hugo --source exampleSite --themesDir .. --destination /tmp/bitblog-public, which failed because hugo is not installed in this environment (error: command not found).
• Attempted a Playwright page screenshot of http://127.0.0.1:1313, which failed with ERR_EMPTY_RESPONSE because no local dev server was running.
• No theme/unit tests were available to run here; recommend building the site with hugo and visually verifying the alignment in a browser once the dev environment is available.

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Codex Task