chore(linkedin-studio): release v0.5.1 — SB-S1 ingest + gold signal

Bump version declarations 0.5.0 → 0.5.1 (plugin.json SSOT + README badge +
CLAUDE.md header + CHANGELOG [0.5.1] entry) for SB-S1. Flip the architecture
SB-S1 row to landed (+ top status). Additive minor: no command/agent/ref/skill
count change; voice-trainer's learning behaviour changes (published-only).
Gate 93/0/0. Polyrepo release (tag v0.5.1 + catalog ref bump) pending push window
+ operator confirm (public open/ remote).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RigJBiRFNtFZKCz21qNbQ4

CLAUDE.md

@@ -1,4 +1,4 @@
-# LinkedIn Studio Plugin (v0.5.0)
+# LinkedIn Studio Plugin (v0.5.1)
 
 > **Version re-baseline (2026-05-31) · M0 landed (2026-06-18, v0.5.0).** Previously numbered 1.0.0–4.1.0; those were pre-release iterations. The honest maturity is **v0.5.0** — **the architecture workstream (M0) is complete: user data now lives in a per-user data dir (`${LINKEDIN_STUDIO_DATA:-$HOME/.claude/linkedin-studio}/`) resolved through one seam per runtime, with automatic idempotent migration on session-start** (see `references/data-path-convention.md`). No command has yet passed the hardening quality-gate, command testing is incomplete, and there is no GUI. The remaining path to **v1.0.0** is three workstreams: **hardening** (every command through the quality-gate), **command testing**, and a **GUI**. The development narrative below is preserved as history.