test(guards): add comprehensive unit tests for contradiction guard

[borjamoskv]

I've added comprehensive unit tests for cortex/guards/contradiction_guard.py satisfying the 3 tests per public function rule and following the pytest setup with an aiosqlite in-memory database and FTS5 virtual table. I also corrected a structural error in contradiction_guard.py where the database context manager was inside the exception block and causing unhandled exceptions if the database was entirely unreadable.

Tests cover:

• detect_contradictions: Happy path (clean), rejection (conflict), and boundary (noise / DB error).
• scan_all_contradictions: Happy path (found pair), boundary (empty DB), and boundary (DB error).

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PR created automatically by Jules for task 4158951521777795611 started by @borjamoskv

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[github-actions]

∞ MÖBIUS — PR Analysis

Metric	Value
Files changed	2
Total changes	238 (+/-)
Complexity	high
Est. review time	30 min
Has tests?	✅
Has Rust changes?	No

Labels applied: security, tests

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Generated by MÖBIUS (Clojure/Babashka) — where code IS data

[codecov]

Codecov Report

❌ Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cortex/guards/contradiction_guard.py	0.00%	11 Missing ⚠️

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