Fix: ember-page-title errors when head format template contains <title>

[FadhlanR]

Previously, the default <title>Boxel</title> lived outside the injectable head zone in index.html, while the realm-server and host mode inject head HTML between data-boxel-head-start and data-boxel-head-end. Enabling the title in the head template would have added a second title, so it stayed commented out. This PR moves the default title into that injectable zone and re-enables it in the head template so injected head replaces the default instead of duplicating it. For custom head templates that omit a title, the default "Boxel" is added automatically so the document always has exactly one <title>.

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Host Test Results

    1 files  ±0      1 suites  ±0   1h 43m 14s ⏱️ -26s
1 925 tests ±0  1 908 ✅ ±0  17 💤 ±0  0 ❌ ±0 
1 940 runs  ±0  1 923 ✅ ±0  17 💤 ±0  0 ❌ ±0 

Results for commit 0ca659d. ± Comparison against base commit 397e601.

♻️ This comment has been updated with latest results.