feat(shims): hand-bridge DelegateDisposable, document non-bridgeable types (#69 session 5)

[ChrisonSimtian]

Summary

Closes out the remaining no-accessible-ctor SHIM001 bucket honestly.

What ships as a bridge:

• Nuke.Common.Utilities.DelegateDisposable — static class re-exposing CreateBracket(Action, Action), CreateBracket<T>(Func<T>, Action<T>), and SetAndRestore<T>. All three return canonical IDisposable, so consumer calls flow through naturally.

What ships as docs (not bridge):

• Fallout.Common.IO.AbsolutePath
• Fallout.Common.Tools.AzureKeyVault.AzureKeyVault
• Fallout.Common.Tools.MSBuild.MSBuildProject

These three are documented as fallout-migrate rename targets in a new "What's NOT covered (and won't be)" README section.

Why those three aren't bridged

Type	Public statics	Why a hand-bridge wouldn't help
AbsolutePath	Create() + 5 const strings	Dominant consumer syntax is AbsolutePath path = "/foo" (implicit conversion) and parent / "child" (operator/). A static class shim can't carry implicit operators, and a subclass shim can't be assignment-compatible with the framework-returned canonical instances. The bridge would be decorative — AbsolutePath.Create(...) is rarely how consumers write it.
AzureKeyVault	none	Internal ctor, framework-constructed only. Zero surface to re-expose.
MSBuildProject	none	Internal ctor, framework-returned only. Zero surface to re-expose.

The fallout-migrate rewrite (Nuke.Common.X.Y → Fallout.Common.X.Y) is the right tool for these — same conclusion as enums, delegates, and structs.

Live impact

Kind	Before (#141)	After
enum	76	76
no-accessible-ctor	8	6 (DelegateDisposable × 2 paths removed)
delegate	14	14
struct	4	4
ambiguous-across-assemblies	4	4
sealed-class	2	2

The 3 remaining unique no-accessible-ctor types match the 3 documented fallout-migrate targets exactly.

Verification

• src/Shims/Nuke.Common builds clean (0 errors)
• tests/Nuke.Common.Shim.Tests builds clean — SampleConsumerBuild.TouchDelegateDisposableShim() exercises both CreateBracket overloads
• The hand-bridge-suppression mechanism from feat(shims): suppress SHIM001 for consumer-bridged types (#69 follow-up) #141 automatically picks up DelegateDisposable, so no SHIM001 fires for it

#69 roadmap status after this

• session 1: ✅ Easy-tier generator + Nuke.Common shim
• session 2: ✅ Static-class method delegation
• session 2b: ⏸️ Sealed-class wrappers — deferred (1 unique attribute, low ROI)
• session 3: ✅ Nuke.Build + Nuke.Components shims
• session 4: ✅ CI host singletons (10 vendors)
• session 4b: ✅ SHIM001 suppression for consumer-bridged types (feat(shims): suppress SHIM001 for consumer-bridged types (#69 follow-up) #141)
• session 5 (this PR): ✅ DelegateDisposable bridge + non-bridgeable docs

The no-accessible-ctor line of attack is now closed — what remains (AbsolutePath, AzureKeyVault, MSBuildProject) is documented fallout-migrate territory.

Test plan

• CI green
• Live shim build: kind: no-accessible-ctor count is 6 (down from 8)
• Consumer trial: using Nuke.Common.Utilities; + DelegateDisposable.CreateBracket(...) compiles

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