feat(hub): external capability registry for PDF/ASR transforms (ADR-0027)

Introduces the External Capability abstraction: platform-registered,
org-enabled document/media transform services invoked as side effects of
an AgentRun. The first concrete capability is pdf_to_md_bundle backed by
MinerU. This lands the contract, schema, adapter interface, and a fully
mock-tested adapter; the real MinerU HTTP client is deferred until
credentials and pricing are confirmed.

Contract:
- spec/Spec/System/Agent/Capability.lean pins ExternalCapability,
  OrganizationCapabilityConnection (reuses ADR-0024 envelope, distinct
  from model-provider connection), and CapabilityInvocation.Authorized
  (workspace containment predicate, ADR-0018). lake build green (41 jobs).
- ADR-0027 records why capability credentials are a separate connection
  type (MinerU/Whisper have their own auth shape, not OpenRouter /v1/models),
  the adapter seam, and what is deferred (capability invocation record,
  pricebook, agent-facing tool discovery).

Schema:
- OrganizationCapabilityConnection + CapabilityCredentialVersion, mirroring
  the Feishu Application Connection shape. Unique by (organizationId,
  capabilityId). Migration 20260718130000 applied.

Adapter (hub/src/capability):
- types.ts: CapabilityId, CapabilityAdapter interface, secret payload,
  CapabilityConnectionUnavailable.
- mineruClient.ts: MineruClient interface + MineruParseResult + errors.
  Real HTTP client deferred; the interface is the seam.
- capabilityConnections.ts: resolveCapabilityCredential — org-scoped,
  fail-closed, reuses LocalSecretEnvelope with purpose="capability".
- pdfToMdBundle.ts: adapter that resolves credential, confines input/output
  to the run workspace (ADR-0018), calls MineruClient, writes md + images
  into workspace, and writes a UsageFact (kind=external_capability,
  quantity=pages, costSource=provider_reported|unknown per ADR-0022).

Tests (7, all green):
- md + images written to workspace, UsageFact attributes pages + cost
- costUsd null -> costSource=unknown (missing cost != zero, ADR-0022)
- no ACTIVE connection -> fail-closed, no fact written
- input/output path escape -> CapabilityPathEscape
- MinerU client error propagates, no fact written
- empty markdown -> parse failure

Deferred (needs operator): MinerU account/API key/pricing, real MineruClient
HTTP implementation, org admin UI for capability connection management,
agent-facing tool exposure (MCP vs built-in).

hub/prisma/migrations/20260718130000_external_capability_connections/migration.sql

@@ -0,0 +1,69 @@
+-- ADR-0027: org-scoped capability connections for external document/media
+-- transforms (PDF→MD, audio/video→text, …). Mirrors the Feishu Application
+-- Connection shape: reuses the ADR-0024 envelope machinery with its own
+-- payload schema and readiness probe, distinct from the model-provider
+-- connection.
+
+CREATE TABLE "OrganizationCapabilityConnection" (
+    "id"                    TEXT                   NOT NULL,
+    "organizationId"        TEXT                   NOT NULL,
+    "capabilityId"          TEXT                   NOT NULL,
+    "status"                "OrganizationConnectionStatus" NOT NULL DEFAULT 'DRAFT',
+    "activeSecretVersionId" TEXT,
+    "activatedAt"           TIMESTAMP(3),
+    "disabledAt"            TIMESTAMP(3),
+    "createdAt"             TIMESTAMP(3)           NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt"             TIMESTAMP(3)           NOT NULL,
+    CONSTRAINT "OrganizationCapabilityConnection_pkey" PRIMARY KEY ("id")
+);
+
+CREATE UNIQUE INDEX "OrganizationCapabilityConnection_organizationId_capabilityId_key"
+  ON "OrganizationCapabilityConnection"("organizationId", "capabilityId");
+CREATE UNIQUE INDEX "OrganizationCapabilityConnection_activeSecretVersionId_key"
+  ON "OrganizationCapabilityConnection"("activeSecretVersionId");
+CREATE INDEX "OrganizationCapabilityConnection_organizationId_status_idx"
+  ON "OrganizationCapabilityConnection"("organizationId", "status");
+CREATE INDEX "OrganizationCapabilityConnection_capabilityId_status_idx"
+  ON "OrganizationCapabilityConnection"("capabilityId", "status");
+
+CREATE TABLE "CapabilityCredentialVersion" (
+    "id"              TEXT                   NOT NULL,
+    "connectionId"    TEXT                   NOT NULL,
+    "version"         INTEGER                NOT NULL,
+    "envelopeVersion" INTEGER                NOT NULL DEFAULT 1,
+    "keyId"           TEXT                   NOT NULL,
+    "envelope"        JSONB                  NOT NULL,
+    "createdByUserId" TEXT,
+    "createdAt"       TIMESTAMP(3)           NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "retiredAt"       TIMESTAMP(3),
+    CONSTRAINT "CapabilityCredentialVersion_pkey" PRIMARY KEY ("id")
+);
+
+CREATE UNIQUE INDEX "CapabilityCredentialVersion_connectionId_version_key"
+  ON "CapabilityCredentialVersion"("connectionId", "version");
+CREATE INDEX "CapabilityCredentialVersion_connectionId_retiredAt_idx"
+  ON "CapabilityCredentialVersion"("connectionId", "retiredAt");
+CREATE INDEX "CapabilityCredentialVersion_keyId_idx"
+  ON "CapabilityCredentialVersion"("keyId");
+CREATE INDEX "CapabilityCredentialVersion_createdByUserId_idx"
+  ON "CapabilityCredentialVersion"("createdByUserId");
+
+ALTER TABLE "OrganizationCapabilityConnection"
+  ADD CONSTRAINT "OrganizationCapabilityConnection_organizationId_fkey"
+  FOREIGN KEY ("organizationId") REFERENCES "Organization"("id")
+  ON DELETE CASCADE ON UPDATE CASCADE;
+
+ALTER TABLE "OrganizationCapabilityConnection"
+  ADD CONSTRAINT "OrganizationCapabilityConnection_activeSecretVersionId_fkey"
+  FOREIGN KEY ("activeSecretVersionId") REFERENCES "CapabilityCredentialVersion"("id")
+  ON DELETE RESTRICT ON UPDATE CASCADE;
+
+ALTER TABLE "CapabilityCredentialVersion"
+  ADD CONSTRAINT "CapabilityCredentialVersion_connectionId_fkey"
+  FOREIGN KEY ("connectionId") REFERENCES "OrganizationCapabilityConnection"("id")
+  ON DELETE CASCADE ON UPDATE CASCADE;
+
+ALTER TABLE "CapabilityCredentialVersion"
+  ADD CONSTRAINT "CapabilityCredentialVersion_createdByUserId_fkey"
+  FOREIGN KEY ("createdByUserId") REFERENCES "User"("id")
+  ON DELETE SET NULL ON UPDATE CASCADE;