Barcode Gen: fix first-save failure and make save errors descriptive

[mishamyte]

Fixes #234

Problem

Creating a barcode (e.g. CODE-128) on a fresh install always failed with a generic "A saving error has occurred":

1. The /ext/apps_data/barcodes folder was only created by init_folder() in free_app() - i.e. on app exit, never at startup - so the very first save had no folder to write into.
2. save_barcode() collapsed every failure (missing folder, duplicate file name, missing SD card, empty fields) into one generic message, and empty name/data returned silently with no feedback at all.

Changes

Folder creation (issue 1)

• init_folder() now runs at startup in barcode_main() and returns whether the folder is usable; save_barcode() calls it again before each save as a safety net (covers mid-session SD removal)
• Real mkdir failures are logged as errors instead of the previous "Barcodes folder already exists" INFO line

Descriptive errors (issue 2)

• Empty name / empty data / no type now show a message instead of silently returning
• One mode-independent clobber guard: saving or renaming over any existing file other than the barcode's own shows "A file with this name already exists" (previously New mode failed with the generic error and Edit mode silently destroyed the other barcode)
• A failed edit-mode rename fails the save with "Could not rename the barcode file" instead of being logged and buried under "File Saved!"; on success the model path is synced so later failures leave no stale path
• All flipper_format_write_* results are checked - a partially written file (e.g. SD card removed mid-save) is reported instead of "File Saved!"
• mkdir failure surfaces as "Cannot access the SD card"
• Save and delete failures return to the create/edit form with the entered data intact instead of dropping to the main menu; the message view got a next_view field (with a safe default) and multiline rendering via elements_multiline_text_aligned
• New message_view_show() helper replaces three hand-rolled copies of the show-message sequence

Housekeeping

• CHANGELOG.md added, backfilled for 1.1-1.4 from repo history and upstream releases; fap_version bumped to 1.5
• Removed the never-defined message_view_free_model() declaration

Testing

• Builds clean with ufbt (Target 7, API 88.0), ufbt format applied
• Installed and launched on a physical Flipper Zero
• Reviewed by code-review, silent-failure, comment-accuracy and simplification passes; all findings addressed or noted

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