[#170] Rename ExternalPromptDefinition to PromptDefinition

[bguidolim]

Summary

The TechPack protocol's declaredPrompts(context:) method returned [ExternalPromptDefinition] — a type defined in ExternalPack/, creating a dependency from the core protocol layer to the adapter layer. Since built-in packs were removed and all packs are now external, the External prefix on prompt types was misleading. This renames and moves the prompt types to TechPack/ where they belong.

Closes #170

Also closes #171 (won't-fix) — the External prefix on other types (e.g. ExternalComponentDefinition, ExternalMCPServerConfig) still serves a purpose: distinguishing YAML schema types from internal engine types that share the same base name.

Changes

• Move ExternalPromptDefinition → PromptDefinition, ExternalPromptType → PromptType, ExternalPromptOption → PromptOption from ExternalPackManifest.swift to new Sources/mcs/TechPack/PromptDefinition.swift
• Update all references across 6 source files, 4 test files, and docs/architecture.md
• Remove redundant explicit Sendable conformances flagged by SwiftFormat on touched files (Swift 6 infers these automatically for value types)

Test plan

• swift test passes locally (637 tests, 56 suites)
• swiftformat --lint . and swiftlint pass without violations
• No runtime behavior change — pure compile-time rename and move

Checklist for engine changes

• Docs updated if behavior changed (docs/architecture.md — protocol signature example updated)

[Copilot]

Pull request overview

Renames and relocates prompt schema types so TechPack.declaredPrompts(context:) no longer depends on ExternalPack/ types, removing an adapter-layer dependency from the core protocol surface and making naming consistent now that all packs are external.

Changes:

• Move/rename prompt schema models to TechPack/ (ExternalPromptDefinition → PromptDefinition, etc.)
• Update call sites in install/configure flow and test mocks to use the new prompt types
• Update architecture docs and remove redundant explicit Sendable conformances on touched types

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
docs/architecture.md	Updates the TechPack protocol example to return [PromptDefinition].
Sources/mcs/TechPack/TechPack.swift	Changes declaredPrompts signature to use PromptDefinition and removes explicit Sendable on touched value types.
Sources/mcs/TechPack/PromptDefinition.swift	Introduces the renamed/moved prompt schema types (PromptDefinition, PromptType, PromptOption).
Sources/mcs/Install/CrossPackPromptResolver.swift	Updates cross-pack prompt grouping/deduplication to use the renamed prompt types.
Sources/mcs/ExternalPack/ExternalPackManifest.swift	Switches manifest prompts to [PromptDefinition]? and removes the old ExternalPrompt* type declarations.
Sources/mcs/ExternalPack/ExternalPackAdapter.swift	Updates declaredPrompts to return [PromptDefinition].
Sources/mcs/ExternalPack/PromptExecutor.swift	Updates prompt execution APIs to accept PromptDefinition.
Sources/mcs/Export/ManifestBuilder.swift	Updates exported manifest prompt construction to use PromptDefinition.
Tests/MCSTests/PromptExecutorTests.swift	Updates prompt fixtures to use PromptDefinition.
Tests/MCSTests/ExternalPackManifestTests.swift	Updates prompt option assertions to PromptOption.
Tests/MCSTests/ExternalPackAdapterTests.swift	Updates adapter prompt fixtures to PromptDefinition.
Tests/MCSTests/CrossPackPromptResolverTests.swift	Updates mock packs and fixtures to use PromptDefinition/PromptOption.

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