Declare each Harness in one file

[SaladDay]

Each Harness is now declared once, in internal/harnessconfig/<package>/declaration.go. One harnessconfig.Declaration holds:

• the kind and label;
• the model providers and native parameter validation;
• the capability descriptor;
• the placements and MCP origins;
• the Harness's own admission restrictions.

Core admission and the Runtime both read that value. Core no longer keeps a parallel per-Harness profile.

Onboarding a Harness now takes

1. One declaration file, internal/harnessconfig/<package>/declaration.go.
2. The adapter's execution code, plus a thin Runtime binding (apps/daemon/internal/agent/<package>/declaration.go) that adds Discover. Discovery can only narrow the declared capabilities, through agent.Narrow and agent.Unavailable, never widen them.
3. The Runtime image under services/core/deploy/<kind>, as before.

make generate-harness-catalog derives everything else from the declarations:

• the Core registry;
• the Runtime declaration list, which is now generated;
• the client ids and labels;
• the installer providers;
• the Harness catalog reference.

Deleted

• services/core/internal/engine: profiles, catalog, enginetest, and the reflect-based completeness machinery.
• internal/harnessconfig/builtin/catalog.json.
• The hand-written adapter list in apps/daemon/internal/cli/agent_discovery.go.
• The per-Harness configuration.go files, which declaration.go replaces.

Behavior

• Admission and rejection results and error codes are unchanged.
• Wording only: Harness restriction messages and the structured-output rejection say "not supported" instead of "not qualified".
• A configured adapter that fails discovery now advertises every capability as Unsupported and no version. It is unavailable either way.
• AGENTS.md: the Runtime–Harness row names the declaration file next to the lifecycle file.

Checks

• go build ./... and go vet ./... pass.
• make check-harness-catalog passes, and make openapi leaves every YAML unchanged.
• make check-names passes.
• scripts/ci_plan_test.py and website/tests/harnesses.test.mjs pass.
• Go tests pass for:
  • internal/harnessconfig/...
  • scripts/harness-catalog
  • contracts/agents-api/v1
  • apps/daemon/internal/agent/...
  • apps/daemon/internal/cli
  • services/core/internal execution, deployment, processconfig, api, sandbox/providers and persistence/postgres/deploymentpg
• New test: TestDiscoveryOnlyNarrowsDeclaration, one per adapter.
• Not run locally: the PostgreSQL-backed integration tests in services/core/tests/integration (they compile and vet; CI runs them) and website/tests/translations.test.mjs (I recomputed the hashes the same way).

Review

No separate blind review on this PR. It will be reviewed in one batch with the follow-up pass-through PRs.

---

^{Need help on this PR? Tag @codesmith-bot with what you need.}