fix: issue #19 UI fixes — nav-bar insets, default tags, post-send auto-return

[kbennett2000]

Fixes #19 — three independent UI issues from the bug report, bundled into one PR (all small, fork-owned UI changes; no frozen-core scan/OCR behavior touched). Happy to split if you'd prefer.

1. Bottom buttons overlapped the Android nav bar

Edge-to-edge is on (targetSdk 36, setDecorFitsSystemWindows(false)), and the page-hub Continue, edit-screen Continue, and settings Save buttons sat under the system nav buttons — you had to tap their top sliver. The capture screens (CameraFragment/CropFragment/OCRFragment) already fix this via UIUtils.adjustMarginForSystemInsets(view, baseDp); this applies that same established pattern to the three screens that were missing it.

Finalize's buttons are top-anchored (the JSON preview fills the bottom), so they don't overlap — intentionally left as-is.

2. Configurable default tags

Tags were hard-coded to sermon. Added a Default tags (comma-separated) field to Settings, stored via SongbirdPrefsHelper (getDefaultTags/setDefaultTags, defaulting to "sermon" so the documented ["sermon"] import default still holds out-of-box; an explicitly-blanked value is honored → empty tag box). EditViewModel.initialize(...) takes the value verbatim and EditFragment passes the configured default, so the edit-screen tag box prefills with it.

3. Send button re-tappable after success → auto-return to start

A successful, clean import now briefly shows the created/skipped result, then clears the session + capture state (mirroring the page hub's existing "start over" reset) and returns to the camera start screen, ready for the next handout. This also stops the Send button being tapped again on an already-imported note. Failures (unreachable / login-rejected / HTTP error / failed > 0) stay put with Send re-enabled for retry.

Verification

• CI gate green: :app:compilePaddleDebugJavaWithJavac :app:testPaddleDebugUnitTest :app:lintPaddleDebug.
• EditViewModelTest updated for the new initialize(..., defaultTags) signature + two new cases (configured default flows through; blank default → no tags).

On-device checklist (why this is a draft)

• Page-hub and edit-screen Continue sit fully above the nav bar and are tappable along their whole height (gesture + 3-button nav).
• Settings shows Default tags; e.g. sermon, majestic view prefills the edit tag box on the next scan; blank-saved → empty box.
• A successful Send briefly shows created/skipped, then auto-returns to the camera with an empty hub (fresh scan starts clean); a failed/unreachable send stays put with Send re-enabled.

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