fix(sentinel): deduplicate configured plugins and polish IT release note

[PythonWoods-Dev]

Implemented both approved final-mile fixes:

Plugin deduplication:
PluginRegistry.load_selected_rules() now deduplicates config.plugins while preserving declaration order, preventing duplicate rule loading and duplicated side effects.
Italian docs polish:
Corrected release-track sentence in docs/it/about/index.md to proper grammar and accents.
Also added regression coverage:

New test ensures duplicate plugin IDs are loaded once and in deterministic order.
Validation:

Full pre-commit pipeline passed (ruff, mypy, pytest, self-check).

[Copilot]

Pull request overview

This PR improves plugin rule loading reliability in Zenzic’s scanner by ensuring configured plugin IDs are deduplicated (preserving declaration order), and polishes a minor Italian documentation sentence about the active release track.

Changes:

• Deduplicate config.plugins in PluginRegistry.load_selected_rules() while preserving order to avoid duplicate rule loading/side effects.
• Add a regression test asserting duplicate plugin IDs are loaded once and deterministically ordered.
• Fix Italian grammar/accents in the docs release-track blurb.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/zenzic/core/rules.py	Deduplicates requested plugin IDs before resolving/loading entry points.
tests/test_rules.py	Adds regression coverage for deduplication + order preservation in plugin loading.
docs/it/about/index.md	Corrects Italian sentence for release-line status wording/accents.

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