Introduce discovery feature: CLI command and core discovery module

[PredictabilityAtScale]

Motivation

• Provide a way for a coding agent to inspect an installed project and propose initial capability candidates so users get a practical starting point after installing CapabilityKit.
• Offer structured discovery output, conservative organization suggestions, and validation to prevent relying solely on README or package metadata.

Description

• Add a new core discovery implementation in packages/core/src/discovery.ts that defines types, validation (validateDiscoveryReport), prompt builder (buildCapabilityDiscoveryPrompt), and organization logic (organizeDiscoveredCapabilityMap).
• Export discovery APIs from packages/core/src/index.ts and add new types for CapabilityDiscoveryReport and related entities.
• Add a discover CLI command in packages/cli/src/index.ts that builds a discovery prompt, runs an external agent via runExternalAgentCommand, parses the JSON report, validates it, organizes suggestions, and supports output options like --output-prompt, --report, --transcript, --dry-run, and --json.
• Wire discovery into capability metadata by updating .capabilities/....capability.yamlstatuses toimplementedand includingimplementation.referencespointing topackages/core/src/discovery.ts` and the new tests.
• Add parsing helpers in the CLI (extractJsonObject, parseDiscoveryReport, formatDiscoveryValidation) to robustly extract and present agent JSON output.

Testing

• Added unit tests packages/core/tests/discovery.test.ts covering buildCapabilityDiscoveryPrompt and validateDiscoveryReport, and packages/core/tests/discoveryOrganization.test.ts covering organizeDiscoveredCapabilityMap and dependency inference.
• Run commands used in verification: npm test -- packages/core/tests/discovery.test.ts, npm test -- packages/core/tests/discoveryOrganization.test.ts, and npm run build, and they completed successfully.

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[chatgpt-codex-connector]

Guard invalid discovery candidate lists

When an external agent returns syntactically valid JSON where candidates is present but not an array, validation records missing-candidates and then immediately tries to iterate that non-array value, throwing before the discover CLI can print the validation errors or write the parsed report. Since this path parses untrusted agent stdout, malformed reports should be reported as invalid instead of crashing during validation.

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