Add accent-insensitive search option

[yyyyyyyan]

Add an "Accent sensitive" toggle to the search menu that allows
diacritics-insensitive matching. When disabled, both the search term and
entry field values are normalized by decomposing to Unicode NFD and
stripping combining marks, so that e.g. "pouzivatel" matches "používateľ"
and vice versa.

This follows the same signal flow as the existing case sensitivity toggle:
SearchWidget toggle -> signal -> DatabaseWidget::setSearchAccentSensitive()
-> EntrySearcher::setAccentSensitive() -> refreshSearch()

AI Disclosure: This PR was developed with assistance from Claude (Opus 4.6). I created an implementation plan in an interactive session with Claude, and Claude executed the initial implementation. After my review and tests I manually refined the code (added ASCII fast path, added some edge-case unit tests, fixed signal/multiplexer race condition in db open sequence).

Fixes #6181

Screenshots

Accent-sensitive search (default, no match for "testingabc" against accented entry):

Accent-insensitive search (unchecked, matches accented entry):

Testing strategy

• Added testAccentInsensitiveSearch to TestEntrySearcher covering:
  • ASCII query matching accented entry and vice versa
  • Field-specific search with accent folding (title:, attachment:, tag:, group:)
  • Exact match (+) and exclude (!) modifiers
  • Case-sensitive combined with accent-insensitive
  • Default accent-sensitive behavior preserved
• All existing tests pass unchanged
• Manual testing with KeePassXC GUI

Type of change

• ✅ New feature (change that adds functionality)

[yyyyyyyan]

A couple of things I'd like to get input on:

1. 60f6259 fixes a bug where EntrySearcher was always constructed with hardcoded defaults, ignoring the user's saved config. I believe this went undetected because all existing toggle defaults were false, matching the constructor defaults, but I bumped into it with the new accentSensitive param defaulting to true. Not sure if this should stay here or be split into a separate issue/PR.

2. I went with accent-sensitive as the default (preserving current behavior), but honestly as a Brazilian Portuguese speaker I'd prefer accent-insensitive as the default. I'd like to know if anyone has any inputs regarding this.

[Copilot]

Pull request overview

Adds a user-facing search toggle to control accent/diacritics sensitivity in the KeePassXC GUI, wiring it through the existing SearchWidget → DatabaseWidget → EntrySearcher flow and implementing Unicode NFD + combining-mark stripping when accent-insensitive matching is enabled.

Changes:

• Add an “Accent sensitive” toggle to the search menu and persist it via a new GUI config key.
• Extend EntrySearcher to support accent-insensitive matching by stripping diacritics from both query terms and searched fields (with an ASCII fast path).
• Add unit tests covering accent-insensitive matching across fields/modifiers and interactions with case sensitivity.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/TestEntrySearcher.h	Adds a new test slot for accent-insensitive search.
tests/TestEntrySearcher.cpp	Introduces comprehensive coverage for accent-insensitive search behavior and modifiers.
src/gui/SearchWidget.h	Adds signal/slot and action member for the new toggle.
src/gui/SearchWidget.cpp	Adds the menu action, persists the setting, and emits the new policy signal on DB changes.
src/gui/DatabaseWidget.h	Adds a slot to apply the accent-sensitivity setting to searching.
src/gui/DatabaseWidget.cpp	Initializes EntrySearcher from config and applies updates via setSearchAccentSensitive().
src/core/Tools.h	Declares Tools::stripDiacritics() utility.
src/core/Tools.cpp	Implements diacritics stripping via NFD decomposition + combining-mark removal (ASCII fast path).
src/core/EntrySearcher.h	Extends constructor/state with accentSensitive and adds setters/getters.
src/core/EntrySearcher.cpp	Applies diacritics stripping to both parsed terms (regex source) and matched fields/lists.
src/core/Config.h	Adds new config key GUI_SearchAccentSensitive.
src/core/Config.cpp	Registers the new config key with default true (accent-sensitive).

[droidmonkey]

I am a fan of making the default more "liberal" and actually remove the option entirely. We already have an "exact match" prefix (ie, +t:acćent). If the user wants exact matching, accents are respected, otherwise the default is no accent matching.

[yyyyyyyan]

Makes sense — implemented this approach. Accent-insensitive is now always the default, the toggle is removed, and + (exact match) forces accent-sensitive matching. So café matches "cafe"/"café", but +café only matches "café".