docs(testing): define Storybook proof ownership architecture

[Vyachean]

Goal

Define one mechanical Storybook and UI-proof ownership model for coding agents, aligned with the current develop branch and the canonical Material Vue library under src/shared/ui/material.

This PR replaces the obsolete draft #170. It defines architecture only; test discovery and test migration will be implemented in separate independently safe PRs.

Architecture decision

• Storybook is an isolated rendering, fixture, and visual-evidence surface, not an FSD layer or product-behavior owner.
• The current UI owner owns its stories and owner-specific browser/visual proof.
• In the Material library, the Material family is the owner.
• Outside Material, the truthful FSD component or cohesive local UI module is the owner.
• Complete cross-owner product scenarios remain centralized in tests/e2e.
• Storybook behavior and visual regression remain independent Playwright lanes.
• Browser proof contains no screenshots; visual proof contains no behavioral success criteria.
• Visual specs remain explicit and colocated; no generated generic story runner is introduced.
• Local naming conventions own ordinary relations; explicit mappings remain for family/module relations that cannot be expressed by one sibling stem and for cross-cutting infrastructure.

The target contract is introduced in docs/testing/storybook.md.

Scope

This PR will contain only:

• the project-wide Storybook ownership contract;
• alignment of docs/testing/architecture.md and docs/testing/migration-plan.md;
• concise repository and scoped agent rules;
• alignment of relevant testing skills;
• a safe migration sequence and pilot selection.

Non-goals

• no Playwright discovery changes;
• no resolver implementation changes;
• no movement of existing browser specs;
• no movement of visual specs or snapshots;
• no correction of existing mixed proof ownership;
• no Storybook title or story-ID normalization;
• no product behavior or public UI API changes;
• no duplication of the Material family workflow;
• no restoration of deleted docs/material-3/storybook.md.

Ownership model

Material

src/shared/ui/material/components/<family>/
├── *.vue
├── *.test.ts
├── *.stories.ts
├── <Family>.browser.spec.ts       # optional
├── <Family>.visual.spec.ts        # optional
└── local fixtures                # rare

Other UI

src/<layer>/<slice>/ui/
├── <Owner>.vue
├── <Owner>.test.ts
├── <Owner>.stories.ts
├── <Owner>.browser.spec.ts        # optional
├── <Owner>.visual.spec.ts         # optional
└── local fixtures                # rare

Product scenarios

tests/e2e/

Planned migration PRs

1. colocated browser discovery pilot using Loading Indicator;
2. remaining Storybook browser-spec migration;
3. colocated visual discovery and snapshot-ownership pilot;
4. remaining visual-spec and baseline migration;
5. proof-ownership cleanup after resolver stability;
6. Storybook catalogue normalization.

Each PR must preserve current commands, broad fail-closed fallback, and regression protection before removing legacy ownership.

Acceptance criteria

• the architecture names one truthful owner for stories, browser proof, visual proof, and product scenarios;
• Material family ownership is consistent with src/shared/ui/material rules and architecture;
• ordinary component, family, foundation, and module ownership are all defined;
• local and explicitly mapped relations are deterministic rather than inferred by agents;
• baseline ownership and add/modify/delete/rename fallback are specified;
• testing architecture and migration policy do not conflict with the new contract;
• agent rules and testing skills route to the same ownership model;
• implementation and mass migration remain outside this PR;
• version is bumped from 0.2.14 to 0.2.15 without dependency changes;
• PR remains draft until the complete documentation/rules diff is reviewed and the current head passes required verification.

Current state

• created from current develop after Material library merge;
• added initial docs/testing/storybook.md;
• bumped version to 0.2.15 while preserving dependencies;
• align canonical testing architecture;
• align migration plan;
• align AGENTS and testing skills;
• complete architecture review;
• run current-head verification.

TEST IMPACT

Changed contracts:

• repository authoring rules for Storybook stories and UI-owned browser/visual proof;
• future ownership and migration sequence for Storybook Playwright specs and snapshots.

Risks:

• conflict with existing testing policy or Material family workflow;
• ambiguous family/module ownership;
• future resolver design being underspecified for rename/delete and snapshots;
• agents interpreting target architecture as already implemented.

Proof owners:

• documentation consistency review;
• instruction compatibility checks after rule/skill updates;
• repository verification selected for the final documentation/rules diff.

Repository impact metadata updates:

• none in this architecture-only PR; resolver metadata changes belong to later implementation PRs.

Task-specific measurements:

• none.

[github-actions]

Preview deployment

• Application: https://mioframe.github.io/pr/173/
• Storybook: https://mioframe.github.io/pr/173/storybook/

This comment is updated automatically on every push to this PR.