fix(config): remove hardcoded Debug paths — thumbnails + Freeplane/FreeMind (#283)

[jsboige]

Summary

• ThumbnailsPathExpression (3 files): Replace hardcoded ../../bin/Debug/netcoreapp3.1/Target/... with Target/... — the path now resolves correctly in both Debug and Release builds
• FreeplanePath / FreeMindPath: Change from machine-specific paths (C:\Users\MYIA\...) to empty string defaults — configurable via JSON, existing guard (string.IsNullOrEmpty + !File.Exists) ensures graceful skip

Before

// MindMapDocumentConfig.cs:172 (same in Fallacy + Virtue variants)
public string ThumbnailsPathExpression { get; set; } = @"../../bin/Debug/netcoreapp3.1/Target/Images/...";
// AssetConverterConfig.cs:244-245
public string FreeplanePath { get; set; } = @"C:\Users\MYIA\AppData\Local\Programs\Freeplane\freeplane.exe";
public string FreeMindPath { get; set; } = @"C:\Program Files (x86)\FreeMind\FreeMind.exe";

After

// Works from both bin/Debug/net9.0 and bin/Release/net9.0
public string ThumbnailsPathExpression { get; set; } = @"Target/Images/density-0/Fallacies-Web-Thumbnails/...";
// Empty defaults — user sets via JSON config or environment
public string FreeplanePath { get; set; } = "";
public string FreeMindPath { get; set; } = "";

Test plan

• dotnet build — 0 error
• dotnet test — 120 pass / 0 fail / 5 skip
• Mind map generation with thumbnails still resolves paths correctly (functional test post-merge)

Fixes HIGH items #1-5 from issue #283. Parent: Epic #278.

🤖 Generated with Claude Code

[myia-ai-01]

LGTM ✅

Review summary:

• ThumbnailsPathExpression (3 files) — Target/... resolves correctly relative to exe working dir (bin/<Config>/net9.0-windows/) in both Debug and Release. Old ../../bin/Debug/netcoreapp3.1/... was triple-wrong (relative, hardcoded Debug, wrong TFM).
• FreeplanePath empty default — verified no .cs consumer (dead config, change is purely cosmetic, zero functional impact).
• FreeMindPath empty default — guarded by string.IsNullOrEmpty(freemindPath) || !File.Exists(freemindPath) at FallacyMindMapDocumentConfig.cs:558 → LogWarning + skip. Safe.
• Tests already use FreeMindPath = "" / FreeplanePath = "" (Tests/MindmapGeneration/*.cs) — convention preserved.

Validation locale:

• dotnet build : 0 erreur (17 warnings préexistants, non liés)
• dotnet test : 120 réussis / 0 échec / 5 ignorés

Note encoding: Le diff ajoute un BOM au début de FallacyMindMapDocumentConfig.cs — harmless mais à surveiller pour cohérence future (PR séparée si on veut normaliser).

Merge en --squash pour clôturer issue #283 et avancer Task 3 d'Epic #278.

[myia-ai-01]

⚠️ Merge bloqué côté ai-01 — GraphQL: myia-ai-01 does not have the correct permissions to execute MergePullRequest.

Testé --squash, --merge, --rebase : tous échouent avec la même erreur. Curieux car PR #281 et #282 ont mergé sans souci ce matin (c4458b40, 7abd4e0a). Permission GraphQL intermittente, peut-être un toggle org-level entre temps.

Action requested @jsboige : merger en --squash quand tu peux. La PR est LGTM (build clean, 120 tests OK, review ci-dessus).

Je continue avec validation PDF visuelle #247/#249/#252 en parallèle.