docs: Align the README settings table with build.properties.ps1

[tablackburn]

Summary

• Removes $PSBPreference.Docs.AlphabeticParamsOrder from the README settings table and from
  the Docs row in instructions/repository-specific.instructions.md. It was removed from the
  module in Update PlatyPS dependency from platyPS v0.14.x to Microsoft.PowerShell.PlatyPS v1.x #105 (issue Update PlatyPS dependency from platyPS v0.14.x to Microsoft.PowerShell.PlatyPS v1.x #105 / PR feat!: Migrate markdown and MAML help to Microsoft.PowerShell.PlatyPS 1.x #173) when help generation moved to
  Microsoft.PowerShell.PlatyPS 1.x, which always sorts parameters alphabetically. It is gone
  from PowerShellBuild/build.properties.ps1 and there is no AlphabeticParamsOrder parameter
  on Build-PSBuildMarkdown, so both files were advertising a setting a consumer cannot set.
• Removes $PSBPreference.Build.Dependencies, found while auditing the rest of the same table.
  It was replaced by the $PSB{TaskName}Dependency variables in Loosen Dependencies #72 (0.7.0), it is absent from
  the defaults, and IB.tasks.ps1 throws a NotSupportedException if a consumer sets it — the
  README already documents the replacement in its own "Modifying task dependencies" section.
• Corrects four Test defaults that documented the parameter defaults of Test-PSBuildPester
  rather than the $PSBPreference values that are actually passed to it, and rewords
  Test.CodeCoverage.OutputFile's description, which claimed the path was relative to the
  Pester test directory and so contradicted its own corrected absolute default.
• Adds a drift guard for the README table, alongside the existing one for the task files.

docs/migration-v0.8-to-v1.0.md is untouched — it documents the removal deliberately.

Corrected defaults

Setting	Documented	build.properties.ps1
Test.OutputFile	$null	[IO.Path]::Combine($env:BHProjectPath, 'testResults.xml')
Test.CodeCoverage.Files	*.ps1, *.psm1	@()
Test.CodeCoverage.OutputFile	coverage.xml	[IO.Path]::Combine($env:BHProjectPath, 'codeCoverage.xml')
Test.CodeCoverage.OutputFileFormat	$null	JaCoCo

Test.CodeCoverage.OutputFile's description read "Output file path (relative to Pester test
directory) where Pester will save code coverage results to", which the corrected absolute
default contradicted. The parenthetical was incomplete rather than wrong — Test-PSBuildPester
does Push-Location -LiteralPath $Path into the test directory before assigning
$configuration.CodeCoverage.OutputPath, so a relative value does resolve against the test
directory — so the cell now states both facts. Test.OutputFile has the same absolute default
and the same behaviour for relative values, but its description makes no relativity claim and
was left alone.

Every row keeps its existing fixed-width column alignment; no untouched row was reflowed.

The drift guard

tests/IBTasks.tests.ps1 already resolves every $PSBPreference path the two task files
reference against the defaults (Describe 'Settings referenced by the task files', added for
#178). Nothing did the equivalent for the README, which is why a setting removed in #105 and one
removed in #72 both survived there. The new Describe 'Settings documented in the README'
parses $PSBPreference.* out of the table rows and resolves each one the same way.

Verified in both directions: with the table as it stands the test passes in isolation
(-FullNameFilter '*README*'), and re-adding the AlphabeticParamsOrder row fails it with
Expected $null or empty, but got 'Docs.AlphabeticParamsOrder'.

Two structural notes:

• The shared setup ($script:defaultPreference and Test-PreferencePath) moved from the first
  drift Describe into a file-level BeforeAll so both blocks can run under a filter
  independently. Nothing else in the existing tests changed.
• The guard has an allow list of four settings — Build.CompileHeader, Build.CompileFooter,
  Build.CompileScriptHeader, Build.CompileScriptFooter. These are documented but
  deliberately absent from the defaults: both task files forward them to Build-PSBuildModule
  only when the consumer has added the key, so defining them would inject empty strings into
  every compiled PSM1.

Not fixed here, reported instead

• The whole Sign section is undocumented in the README. build.properties.ps1 defines 13
  Sign.* settings plus 3 under Sign.Catalog, and the README settings table covers none of
  them. That is a section to write, not a row to fix, so the new test only asserts the
  documented-to-defined direction; the reverse would fail today. The signing settings are
  covered in instructions/repository-specific.instructions.md.
• The README's task-dependency table is missing the signing chain. It stops at
  $PSBPublishDependency and omits $PSBSignModuleDependency, $PSBBuildCatalogDependency,
  $PSBSignCatalogDependency, and $PSBSignDependency. Same root cause as the above; those
  four are listed in instructions/repository-specific.instructions.md.
• instructions/repository-specific.instructions.md names the migration guide as
  docs/migration/v0.8-to-v1.0.md; the file on disk is docs/migration-v0.8-to-v1.0.md. Not a
  settings drift, so left out of this diff.

No CHANGELOG entry: the removal is already logged under #105, and this is a correction to the
documentation of an already-logged change.

Test plan

• ./build.ps1 -Task Test — 484 passed, 0 failed, 3 skipped (483/0/3 on main, plus the
  one test added here). Analyze clean.
• New guard passes in isolation and fails when the removed row is re-added.
• grep -rn AlphabeticParamsOrder leaves matches only in CHANGELOG.md and
  docs/migration-v0.8-to-v1.0.md, both of which document the removal on purpose, plus the
  new test's explanatory comment.

Breaking changes

None. Documentation and tests only.

🤖 Generated with Claude Code

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Test Results

    4 files  ±0    764 suites  +4   2m 42s ⏱️ +23s
  486 tests +1    483 ✅ +1   3 💤 ±0  0 ❌ ±0 
1 948 runs  +4  1 881 ✅ +4  67 💤 ±0  0 ❌ ±0 

Results for commit 2aa6c97. ± Comparison against base commit a64ebc8.