Fix RealDataTestsBase cross-worktree test collisions

[johnml1135]

Summary

• RealDataTestsBase (backing RenderBaselineTests, RenderBenchmarkTestsBase, and subclasses) resolved its scratch test-project directory via FwDirectoryFinder.ProjectsDirectory, a per-machine registry value that's correct for the shipping app (one shared Projects folder machine-wide) but means every git worktree of this repo collides on the same physical integration_test_data folder when running these tests.
• Symptom: System.InvalidOperationException: Refusing to delete '...\integration_test_data' because the test sentinel file '.fieldworks-real-data-test-project' is missing — one worktree's test run deletes/rewrites another's project mid-run.
• Fix (scoped entirely to this test fixture, FwDirectoryFinder's production API is untouched):
  1. DbDirectory() now resolves under this checkout's own SourceDirectory/../DistFiles/Projects, matching the pattern already used by other real-cache test fixtures in this repo (ConfiguredXHTMLGeneratorTests, RecordListTests, etc.).
  2. The project name is suffixed with a short hash of the worktree's SourceDirectory, because FwNewLangProjectModel.CheckForUniqueProjectName — correct, unrelated production logic for the real "New Project" wizard — checks name uniqueness against the shared ProjectsDirectory regardless of where this fixture's files live, so a fixed name still collided across worktrees. The suffix is stable within a worktree (preserving the mutex-guarded "reusable project" perf intent) but unique across worktrees.

Found and fixed while running CI locally as part of an unrelated PR #964 review — see that PR's PR_964_review.md §15 for the full investigation trail.

Test plan

• RenderBaselineTests + RealDataTestsBaseCleanupTests (9 tests): went from 8/9 failing with the collision error to 9/9 passing.
• Full ./test.ps1 CI-equivalent run

🤖 Generated with Claude Code

---

This change is 

[github-actions]

NUnit Tests

    1 files  ±0      1 suites  ±0   10m 32s ⏱️ +28s
4 299 tests ±0  4 226 ✅ ±0  73 💤 ±0  0 ❌ ±0 
4 308 runs  ±0  4 235 ✅ ±0  73 💤 ±0  0 ❌ ±0 

Results for commit 7a61c4f. ± Comparison against base commit fb4c99d.

[jasonleenaylor]

@jasonleenaylor reviewed 1 file and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on johnml1135).

[jasonleenaylor]

A commit comment that contains all the comments also present in the code is a bit much. Please make sure we commit a much more results focused comment rather than details of the solution and maybe shorten the code comments as well.

@jasonleenaylor made 2 comments.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on johnml1135).

---

Src/Common/RootSite/RootSiteTests/RealDataTestsBase.cs line 169 at r1 (raw file):

			// delete or rewrite another's mid-run). Anchor to this checkout's own DistFiles/Projects
			// instead - the same SourceDirectory-derived, registry-free pattern already used by other
			// real-cache test fixtures in this repo (e.g. ConfiguredXHTMLGeneratorTests, RecordListTests).

This comment is awefully long and wordy, wouldn't mind a pass at tightening it up.