chore(WebUI Smoke CLI): introduce @smoke tag convention for e2e specs

## Parent

- Epic: [FR-2871](https://lablup.atlassian.net/browse/FR-2871)
- Spec Task: [FR-2872](https://lablup.atlassian.net/browse/FR-2872)
- Spec: `.specs/FR-2871-webui-smoke-cli/spec.md` § FR-A

## Goal

Introduce a Playwright `@smoke*` tag taxonomy and apply it to a starter set of existing e2e specs so the Smoke CLI can select a stable, single-account subset.

## Acceptance criteria

- [ ] Document the tag taxonomy in `E2E-TEST-NAMING-GUIDELINES.md`:
- `@smoke` — base smoke set; single account; must complete in 5–10 minutes
- `@smoke-admin` — admin-only signals (user mgmt, resource policies, agent list)
- `@smoke-user` — end-user signals (session lifecycle, vfolder, environment list)
- `@smoke-any` — role-agnostic
- `@smoke-extended` — opt-in via `--profile extended`
- [ ] Tag at least the following existing specs (no-op functional change):
- Login / logout / token expiry
- Dashboard render
- Session lifecycle (create → running → terminate)
- VFolder create / upload / download / delete
- Environment & image list
- (admin) User list, resource policy list, agent list
- [ ] `pnpm --filter ./e2e exec playwright test --grep @smoke --list` lists at minimum the specs above.
- [ ] No existing e2e CI job changes behaviour (tags are additive metadata).

## In scope

- `E2E-TEST-NAMING-GUIDELINES.md`
- `e2e/tests/**` — adding tag annotations to existing `test(...)` titles (no behavioural change)

## Out of scope

- Creating any new test (covered by FR-J)
- Modifying e2e fixtures or utilities (covered by FR-F)
- Modifying any CI workflow

## Test plan

- Run `pnpm --filter ./e2e exec playwright test --grep @smoke --list` and confirm the listed specs cover all categories above.
- Run the existing e2e CI workflow once (no grep) and confirm the run count is identical to pre-change.

JIRA Issue: FR-2875

[FR-2871]: https://lablup.atlassian.net/browse/FR-2871?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ
[FR-2872]: https://lablup.atlassian.net/browse/FR-2872?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

Read E2E-TEST-NAMING-GUIDELINES.md and inspect the existing test titles under e2e/tests/**. Add the specified @smoke taxonomy annotations without changing behavior, then run pnpm --filter ./e2e exec playwright test --grep @smoke --list to verify the required categories appear. Confirm the existing e2e CI run count remains unchanged.

Written by the indexing model from the issue text.