feat(architecture): [EoS/claude] drive claude through the imperative adapter + descriptor-driven hostBehaviors (#2086)

Fold Claude Code's install/uninstall onto the Embeddable Orchestration System
(ADR-1239 Phase D). claude is GSD's tier-1 reference host, but its install path
was still driven by 13 hardcoded `runtime === 'claude'` string-equality branches
scattered across bin/install.js rather than the public Host-Integration Interface.

- Route install()/uninstall() through `createImperativeAdapter({runtime})` — the
  adapter delegates to the SAME installRuntimeArtifacts/uninstallRuntimeArtifacts
  engine calls, so output is byte-identical (proven pre/post, both scopes).
- Replace all 13 `runtime === 'claude'` / `runtime !== 'claude'` branches with
  descriptor-driven `runtime.hostBehaviors` lookups on capabilities/claude/
  capability.json (attributionSource, authorsCanonicalWorkflow, localInstallStyle,
  permissionsSchema, settingsFileByScope, sourceMarkerFile, agentFrontmatterExtensions,
  ownsClaudePaths, nativeModelAliases, skillsGlobalOnboarding). Behavior is
  identical; the brittle string-equality coupling (the add-a-host tax) is gone.
- Single-source the scattered literal 'claude' defaults/rosters behind DEFAULT_RUNTIME.
- Extend golden-install-parity to assert the claude LOCAL legacy layout is
  byte-identical too (AC1 "both scopes"); exclude the platform-varying
  settings.local.json (same reason settings.json is excluded).
- New tests/claude-imperative-reference.test.cjs: adapter kind, programmatic-cli
  profile, fail-closed negotiation on a corrupted/partial descriptor, and an AC2
  source guard that no `runtime === 'claude'` branch remains.

No user-visible install-output change (internal architecture only).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.changeset/2086-eos-claude-imperative-adapter.md

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+---
+type: Changed
+pr: 2086
+---
+**Internal: Claude Code's installer is now driven through the public Host-Integration Interface (ADR-1239 / EoS).** `bin/install.js` routes `claude` install/uninstall through the imperative adapter (`createImperativeAdapter`) instead of calling the engine directly, and its 13 hardcoded `runtime === 'claude'` / `runtime !== 'claude'` branches are folded into descriptor-driven `runtime.hostBehaviors` on `capabilities/claude/capability.json` (permission schema, `settings.local.json` scope routing, `.gsd-source` marker, effort frontmatter, canonical-workflow authorship, and more). Install/uninstall output is **byte-identical** for both the global skills layout and the local legacy layout (golden-parity asserted for both scopes); no other runtime changes. Removes the "add-a-host tax" of scattered string-equality checks for the tier-1 reference host. No user-facing change. (#2086)