nightshift/bug: editing titled snippets with colons corrupts data

[perandre]

Bug

EditSnippetRow.saveChanges() in Sources/EditSnippetRow.swift corrupts snippet titles that contain ": ".

When editing a snippet with title "Note: Important" and value "some data", the edit field is pre-filled with "Note: Important: some data". On save, SnippyParser.parse() splits at the first ": ", producing title="Note" and value="Important: some data" — silently destroying the original title.

Repro

1. Add a snippet by typing Note: Important: some data (creates title="Note", value="Important: some data")
2. Edit the snippet — field shows "Note: Important: some data", which is correct
3. Press Return without changing anything
4. The title is now "Note" and value is "Important: some data" — the round-trip was lossless here because the title didn't have ": "

Now the problematic case:

1. Programmatically or via JSON have a snippet with title="Note: Important", value="data"
2. Edit it — field shows "Note: Important: data"
3. Press Return — SnippyParser.parse() splits at first ": ", producing title="Note", value="Important: data"
4. The title has been corrupted from "Note: Important" to "Note"

Fix

EditSnippetRow now tracks whether the snippet originally had a title (originalTitleLength). When it did, saveChanges() splits at the last ": " instead of re-parsing through SnippyParser, which always splits at the first. This preserves titles containing colons while keeping the single-field editing UX.

For snippets that originally had no title, SnippyParser is still used (first ": " split), matching the behavior of AddSnippetRow.