feat(cli): add openspec config command for global configuration management

openspec/changes/archive/2025-12-21-add-config-command/design.md

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+## Context
+
+The `global-config` spec defines how OpenSpec reads/writes `config.json`, but users currently must edit it by hand. This command provides a CLI interface to that config.
+
+## Goals / Non-Goals
+
+**Goals:**
+- Provide a discoverable CLI for config management
+- Support scripting with machine-readable output
+- Validate config changes with zod schema
+- Handle nested keys gracefully
+
+**Non-Goals:**
+- Project-local config (reserved for future via `--scope` flag)
+- Complex queries (JSONPath, filtering)
+- Config file format migration
+
+## Decisions
+
+### Key Naming: camelCase with Dot Notation
+
+**Decision:** Keys use camelCase matching the JSON structure, with dot notation for nesting.
+
+**Rationale:**
+- Matches the actual JSON keys (no translation layer)
+- Dot notation is intuitive and widely used (lodash, jq, kubectl)
+- Avoids complexity of supporting multiple casing styles
+
+**Examples:**
+```bash
+openspec config get featureFlags              # Returns object
+openspec config get featureFlags.experimental # Returns nested value
+openspec config set featureFlags.newFlag true
+```
+
+### Type Coercion: Auto-detect with `--string` Override
+
+**Decision:** Parse values automatically; provide `--string` flag to force string storage.
+
+**Rationale:**
+- Most intuitive for common cases (`true`, `false`, `123`)
+- Explicit override for edge cases (storing literal string "true")
+- Follows npm/yarn config patterns
+
+**Coercion rules:**
+| Input | Stored As |
+|-------|-----------|
+| `true`, `false` | boolean |
+| Numeric string (`123`, `3.14`) | number |
+| Everything else | string |
+| Any value with `--string` | string |
+
+### Output Format: Raw by Default
+
+**Decision:** `get` prints raw value only. `list` prints YAML-like format by default, JSON with `--json`.
+
+**Rationale:**
+- Raw output enables piping: `VAR=$(openspec config get key)`
+- YAML-like is human-readable for inspection
+- JSON for automation/scripting
+
+### Schema Validation: Zod with Unknown Field Passthrough
+
+**Decision:** Use zod for validation but preserve unknown fields per `global-config` spec.
+
+**Rationale:**
+- Type safety for known fields
+- Forward compatibility (old CLI doesn't break new config)
+- Follows existing `global-config` spec requirement
+
+### Reserved Flag: `--scope`
+
+**Decision:** Reserve `--scope global|project` but only implement `global` initially.
+
+**Rationale:**
+- Avoids breaking change if project-local config is added later
+- Clear error message if someone tries `--scope project`
+
+## Risks / Trade-offs
+
+| Risk | Mitigation |
+|------|------------|
+| Dot notation conflicts with keys containing dots | Rare in practice; document limitation |
+| Type coercion surprises | `--string` escape hatch; document rules |
+| $EDITOR not set | Check and provide helpful error message |
+
+## Open Questions
+
+None - design is straightforward.

openspec/changes/archive/2025-12-21-add-config-command/proposal.md

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+## Why
+
+Users need a way to view and modify their global OpenSpec settings without manually editing JSON files. The `global-config` spec provides the foundation, but there's no user-facing interface to interact with the config. A dedicated `openspec config` command provides discoverability and ease of use.
+
+## What Changes
+
+Add `openspec config` subcommand with the following operations:
+
+```bash
+openspec config path                          # Show config file location
+openspec config list [--json]                 # Show all current settings
+openspec config get <key>                     # Get a specific value (raw, scriptable)
+openspec config set <key> <value> [--string]  # Set a value (auto-coerce types)
+openspec config unset <key>                   # Remove a key (revert to default)
+openspec config reset --all [-y]              # Reset everything to defaults
+openspec config edit                          # Open config in $EDITOR
+```
+
+**Key design decisions:**
+- **Key naming**: Use camelCase to match JSON structure (e.g., `featureFlags.someFlag`)
+- **Nested keys**: Support dot notation for nested access
+- **Type coercion**: Auto-detect types by default; `--string` flag forces string storage
+- **Scriptable output**: `get` prints raw value only (no labels) for easy piping
+- **Zod validation**: Use zod for config schema validation and type safety
+- **Future-proofing**: Reserve `--scope global|project` flag for potential project-local config
+
+**Example usage:**
+```bash
+$ openspec config path
+/Users/me/.config/openspec/config.json
+
+$ openspec config list
+featureFlags: {}
+
+$ openspec config set featureFlags.enableTelemetry false
+Set featureFlags.enableTelemetry = false
+
+$ openspec config get featureFlags.enableTelemetry
+false
+
+$ openspec config list --json
+{
+  "featureFlags": {}
+}
+
+$ openspec config unset featureFlags.enableTelemetry
+Unset featureFlags.enableTelemetry (reverted to default)
+
+$ openspec config edit
+# Opens $EDITOR with config.json
+```
+
+## Impact
+
+- Affected specs: New `cli-config` capability
+- Affected code:
+  - New `src/commands/config.ts`
+  - New `src/core/config-schema.ts` (zod schema)
+  - Update CLI entry point to register config command
+- Dependencies: Requires `global-config` spec (already implemented)