refactor(linkedin-studio): move agent fasit fixtures + tests out of agents/ (v0.5.3)

The 6 long-form-review fasit fixtures (agents/fixtures/*-cases.md) were registered
by Claude Code as junk `fixtures:*` agents because agents/ is scanned recursively.
They are test fixtures, not capabilities. Moved them + their 6 lint tests to
tests/ + tests/fixtures/ and retargeted the 5 agent fasit-refs. Count-neutral
namespace hygiene (ls agents/*.md still 19).

- agents/fixtures/*-cases.md            -> tests/fixtures/        (6)
- agents/__tests__/*-fixture.test.mjs   -> tests/                 (6; ../fixtures -> ./fixtures)
- 5 agent refs ${CLAUDE_PLUGIN_ROOT}/agents/fixtures -> /tests/fixtures
- version-sync 0.5.2 -> 0.5.3 (plugin.json / README badge / CLAUDE.md / CHANGELOG)

Verify: fixture-lint 35/35 at new path; render 20/20, hooks 139/139; test-runner 109/0/0.
Reinstall/reload required for the 6 spurious agents to leave the registry.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CrTb8ktf1XZWEVwgz5MTTo

CHANGELOG.md

@@ -5,6 +5,16 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.5.3] - 2026-06-24
+
+### Changed — registration hygiene: agent fasit fixtures moved out of `agents/`
+
+**Stops Claude Code from registering 6 spurious agents.** The six long-form-review fasit fixtures lived in `agents/fixtures/*-cases.md`; because Claude Code scans `agents/` recursively, each was registered as a junk `fixtures:*` agent (`fixtures:content-reviewer-cases`, …). They are test fixtures, not capabilities. **Count-neutral** (no real agent/command/reference/skill change; `ls agents/*.md` still 19) — pure namespace hygiene.
+
+- **Moved** the 6 fasit fixtures `agents/fixtures/*-cases.md` → `tests/fixtures/*-cases.md`, and their 6 lint tests `agents/__tests__/*-fixture.test.mjs` → `tests/*-fixture.test.mjs` (co-located; each test's relative fixture path retargeted `../fixtures/` → `./fixtures/`). `agents/fixtures/` and `agents/__tests__/` are now removed.
+- **Retargeted** the 5 agent fasit-refs (`content`/`language`/`persona`/`editorial`/`fact-reviewer`) from `${CLAUDE_PLUGIN_ROOT}/agents/fixtures/…` to `${CLAUDE_PLUGIN_ROOT}/tests/fixtures/…`.
+- **Tests.** Fixture-lint 35/35 at the new path (`node --test 'tests/*.test.mjs'`); render 20/20, hooks 139/139 unaffected; gate `scripts/test-runner.sh` green (counts + version-consistency). Reinstall/reload required for the 6 spurious agents to disappear from the registry.
+
 ## [0.5.2] - 2026-06-23
 
 ### Added — SB-S2: the evolution loop (second-brain arc)