Store run artifacts outside project repositories by default

[ElbertePlinio]

Problem

PickLab currently writes generated run artifacts to <project>/.picklab/runs/ by default. Screenshots and manifests then appear in the target repository's source-control view, even though they are runtime output rather than project source.

PickForge already defaults per-project runtime data outside repositories. PickLab should follow the same model under the shared Pickforge company root.

Proposed outcome

Default PickLab run storage to:

~/.pickforge/picklab/projects/<projectId>/runs/<runId>/

Use the platform home-directory equivalent on non-Linux systems. Keep each project's runs isolated with a stable project ID derived from its canonical path.

Storage modes:

• home (default): Pickforge company root above
• project-local (explicit opt-in): <project>/.picklab/runs/
• custom (explicit absolute path)

Keep project configuration at <project>/.picklab/config.json; only generated runtime artifacts move by default.

Compatibility

• New runs write only to the resolved storage location.
• Existing <project>/.picklab/runs/ data remains readable by artifact list/show/report/resource flows.
• Do not automatically move or delete existing runs.
• Preserve PICKLAB_HOME as the PickLab-root override; its default becomes ~/.pickforge/picklab.
• Document any one-time behavior affecting existing ~/.picklab global config, agents, or sessions. Prefer a non-destructive read fallback rather than silently orphaning them.

Acceptance criteria

• A default screenshot/run creates no generated files inside the target repository.
• Default runs are isolated under ~/.pickforge/picklab/projects/<projectId>/runs/.
• The same canonical project path resolves to the same project ID; different paths do not collide.
• CLI and MCP artifact create/list/show/report/resource flows use the same resolver.
• project-local restores the current <project>/.picklab/runs/ behavior when explicitly configured.
• custom rejects ambiguous/unsafe configuration (for example, a missing path or a relative path if absolute paths are required).
• Existing project-local runs remain discoverable without an automatic migration.
• PICKLAB_HOME overrides work in tests and real CLI/MCP usage.
• README/config examples explain the default, project-local opt-in, custom storage, legacy behavior, and source-control impact.
• docs/releases/UNRELEASED.md records the user-visible default change.

Agent plan

Goal: move generated PickLab runs out of repositories by default while preserving explicit local storage and non-destructive access to legacy runs.

Checklist:

• Add a core storage resolver for home/project-local/custom modes and stable per-project IDs.
• Route run creation and artifact lookup through the resolver across core, CLI, and MCP.
• Add legacy project-local read fallback without legacy writes or automatic deletion/moves.
• Handle the ~/.picklab → ~/.pickforge/picklab default-root transition for config, agents, and sessions without silently losing existing state.
• Add regression tests for default repo cleanliness, project isolation, overrides, explicit local mode, custom paths, and legacy discovery.
• Update README, config examples, and unreleased notes.
• Run focused tests, then bun run typecheck, bun run test, and bun run build.
• Open one focused PR and complete review.

Validation:

• bun run test packages/core/test/paths.test.ts packages/core/test/run.test.ts packages/core/test/config.test.ts
• focused CLI/MCP artifact tests added by this change
• bun run typecheck
• bun run test
• bun run build
• manual smoke from a temporary Git repository: create a run and verify git status --short stays clean

PR plan: one PR. The resolver, writers, readers, compatibility behavior, and docs are tightly coupled; splitting would leave an inconsistent storage contract.

Feature flag: not needed if this ships as one backward-compatible change in the next release.

Current status: Planned
Next action: implement the storage resolver and regression tests.