Add the possibility to create tags in text

[LAfricain]

The idea is very simple, it is to do in Xiphos what Ezra project does.
That means, create tags with Ref of the Biblical text.

[karlkleinpaste]

i'm not going to start reading from scratch about yet another bible project.
context: what kind of tags, where placed, how referenced, and in what way useful.

[LAfricain]

Ok I'll come back with more information.

[LAfricain]

My idea would be to convert the current bookmarks tab into a tags tab. Since tags can function as bookmarks but not the other way around. What we would add is that tagged/bookmarked lines could be highlighted in a specific color, and that color would be displayed to the left of the tag group.

[LAfricain]

Work Plan: Bookmarks → Tags Tab Refactor (Xiphos)

Closes: #968 (Add tags to text) · Closes: #685 (Add color to bookmark folders)

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Summary

Convert the existing Bookmarks tab into a Tags tab. Tags are a strict superset of bookmarks: every bookmark can be expressed as a tag entry belonging to a named, color-coded group. The inverse is not true, so migrating in this direction loses nothing and gains multi-category annotation and visual highlighting in the reading view.

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Rationale

Feature	Bookmarks	Tags
Navigate to a verse	✔	✔
Group by topic	—	✔
Color per group	—	✔ (fixes #685)
Highlight verse in text	—	✔ (fixes #968 visually)
One verse → multiple categories	—	✔
Backward-compatible with existing data	—	✔ (see migration)

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Scope

Phase 1 — Data model & storage

Extend the existing bookmark XML format with a color attribute on group/folder nodes.

<!-- Before -->
<folder title="Messianic prophecies">
  <bookmark ref="Isa 7:14"/>
</folder>

<!-- After -->
<taggroup title="Messianic prophecies" color="#378ADD">
  <tag ref="Isa 7:14"/>
</taggroup>

• Keep the old element names as aliases during a transitional read path so existing user files load without error.
• A verse may belong to multiple tag groups (one-to-many relationship).

Phase 2 — Automatic migration

• On first launch after the update, silently convert existing bookmark XML to the new tag format.
• All migrated entries are placed in a group called "Bookmarks (migrated)" with a neutral gray color.
• No data loss; no user action required.
• Migration is a one-time, non-destructive operation — the original file is backed up as bookmarks.xml.bak.

Phase 3 — UI: Tags panel

Replace the Bookmarks tab with a Tags tab. The panel layout:

• Toolbar: + New tag group button, opens a dialog with a name field and a color picker.
• Tag groups: collapsible rows, each showing a colored dot on the left, the group name, and a verse count badge on the right.
• Tag entries: listed under each group, showing the canonical reference (e.g. Gen 1:1). Right-click context menu → Remove / Go to verse.
• Color picker: right-click on a group → Edit color opens a GTK color chooser dialog. The chosen color is stored in the XML and immediately reflected in the panel and in the reading view.

Phase 4 — Visual highlighting in the reading view

When a verse belongs to one or more tag groups, the reading view shows:

• A colored bar (4 px wide) on the left edge of the verse row, using the tag group color.
• A subtle background tint on the verse text (≈10–13 % opacity of the group color).
• Color dot badges on the right side of the row — one per tag group the verse belongs to.
• For verses belonging to multiple groups: the bar is split vertically into segments, one color per group; badges stack horizontally.

Highlighting is rendered at display time from the tag data — no changes to the underlying Bible module text.

Phase 5 — Tagging workflow

Two ways to tag a verse:

1. From the reading view: right-click on a verse → Add to tag group… → pick an existing group or create a new one.
2. From the Tags panel: drag a verse reference into a group, or use Add verse in the group context menu.

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Non-goals (out of scope for this iteration)

• Full-text search within tags.
• Syncing or exporting tags to external formats (OSIS, etc.).
• Tagging arbitrary text spans within a verse (only whole-verse tagging for now).

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UI mockup

See the attached mockup (HTML file). Key design decisions visible there:

• The left panel mirrors the current Bookmarks panel structure so the transition is familiar.
• The migrated bookmarks group uses a gray dot to visually distinguish legacy data.
• Multi-tag verses show a split bar and stacked dot badges without cluttering the text.

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Files likely to be modified

File	Change
src/bookmarks.*	Rename/extend to tags.*; add color field to group struct
src/main_window.*	Rename tab label; wire up new tag panel widget
src/bible_text_window.*	Add per-verse highlight rendering based on tag data
data/bookmarks.xml (user data)	Schema extended; migration script runs once on startup
ui/bookmarks.glade (or equivalent)	Update panel layout; add color dot and color picker

[LAfricain]

Other issue almost related #701