feat(app): experimental AvaloniaEdit renderer for Raw XML and Stream windows

[simtel12]

Summary

• Generalizes the experimental AvaloniaEdit-backed GameTextEditor control (previously game-window-only, behind useeditorgamewindow) behind a new ITextEditorHost contract, and extends it to the Raw XML and Stream windows.
• Adds useeditorrawxmlwindow and useeditorstreamwindow config keys (default off, read once at dock-layout build time, same experimental contract as the existing game-window flag). GenieDockFactory selects EditorRawXmlTool/EditorStreamTool vs. the legacy RawXmlTool/StreamTool per flag — one useeditorstreamwindow flag governs all 12 Stream instances.
• Colorizing and link generation are opt-in per host (ITextEditorHost.EnableColorizing / EnableLinks): on for Game/Stream, off for Raw XML, which stays a plain verbatim dump.
• RawXmlViewModel.Lines moves from ObservableCollection<string> to ObservableCollection<TextLine>, matching GameTextViewModel/StreamBuffer, so the shared renderer has one consistent line type across all three window kinds.
• Adds MainWindowViewModel's dataDirectoryOverride test seam (isolates data-dir discovery for tests without touching real per-user AppData) and new coverage: DataDirectoryOverrideTests, DockFactoryEditorWindowTests, EditorRawXmlWindowConfigTests, EditorStreamWindowConfigTests.

All flags default off — with them off, the legacy per-line ItemsControl rendering is untouched and byte-for-byte the same code path as before.

Test plan

• dotnet build src/Genie.App/Genie.App.csproj — succeeds
• dotnet test tests/Genie.Core.Tests — 1147 passed
• dotnet test tests/Genie.App.Tests — 81 passed, including the new editor-window/dock-factory/data-directory-override coverage

[monil2233]

Reviewed against source and verified locally — build 0 warnings, full suites green (Core 1147, App 81). The generalization follows the #200 pattern faithfully: type-based template selection with the editor templates placed above the legacy ones, flags read once at layout build, config keys registered in the dump/categories/setter, and with both flags off the legacy path is untouched (the only legacy-path edit is the Raw XML ItemsControl retarget from x:String to TextLine, visually identical).

What I checked beyond the diff:

• Per-window highlight scoping survives the shared renderer: GameLineEntry passes each line's own Window into DefaultHighlights.BuildStyleMap, so editor-mode Stream windows keep the same scoping semantics as the legacy renderer.
• The CopyAll/SaveAs call sites correctly follow the Lines type change.
• The dataDirectoryOverride seam mirrors GenieCore's existing UseExplicitRoot — good to finally have dock-factory coverage that can't touch real AppData.

Three notes, none blocking:

1. The one real caution before these flags ever default on: GameLineEntry builds its style map eagerly, and BuildStyleMap fires highlight sound/TTS as a side effect. RebuildAll (re-attach / Reset) and ReplaceLine (rules repaint) reconstruct every entry, which can re-fire alerts for the whole scrollback. That trait came with #200, but this PR multiplies the exposure across 12 stream windows — Combat especially. Worth a follow-up where only Append fires alerts.
2. The new RawXmlViewModel.Lines doc comment cites "(#274)" — that's the automapper config-keys issue; should read #296 (or #200). I'll fix that in a follow-up.
3. Heads-up: this overlaps your draft #258 in GameTextEditor.cs (Subscribe/Unsubscribe and Find wiring) — whichever lands second needs a small rebase, and once #258 is ready, its search-panel behavior on editor Stream windows is worth a re-look.

Merging. Thanks — this is exactly the follow-on flagged in #200, and the flag-off isolation story held up under review.