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

CHANGELOG.md

@@ -5,6 +5,17 @@ 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).
 
+## [0.5.1] - 2026-06-23
+
+### Added — SB-S1: ingest + the published gold signal (second-brain arc)
+
+**The second slice of the second-brain arc.** Captures the user's *actual published posts* into `ingest/published/` tagged `provenance=published` — the gold signal that voice/profile learning is allowed to learn from — and wires the learning surface to that signal **only**, never to AI-drafted content (the model-collapse guard). **Non-breaking** (additive minor): no command/agent/reference/skill count changes; a shipped agent's learning behaviour changes (`voice-trainer`).
+
+- **Ingest data layer** (`scripts/brain/src/ingest.ts`): a `PublishedRecord` file-per-post grammar (fixed 5-line header + `---` sentinel + verbatim body, no YAML) with a `parse ∘ serialize` identity; a content-hash id `mintContentId = sha256(VERBATIM body)[:12]` — byte-identity dedup, so two structurally-different posts never collide and a differing body is never silently dropped.
+- **`brain` CLI** grows `ingest --file <path>` / `ingest --scan-inbox` (top-level `*.md`, skips dotfiles, non-destructive, idempotent, create-on-demand) and `published list` (surfaces `provenance` so ai-draft leakage is visible). The existing `init` is preserved.
+- **Published-only invariant wired + gate-enforced.** `agents/voice-trainer.md` reads `ingest/published/` as its primary gold source, keeps `voice-samples/` as a human tributary (not reshaped), forbids `provenance=ai-draft`, and fences the auto-append trap. A new structure-lint section (Brain Published-Only Invariant) enforces the wiring with exact-literal greps + a non-vacuity self-test.
+- **Tests.** brain suite 34 → 63 (`ingest` 14 + `publish` 9 + `cli` 6); gate `scripts/test-runner.sh` 90 → 93/0/0 (`BRAIN_TESTS_FLOOR` 34→63, assertion floor 75→78). No automatic `brain/profile.md` mutation (the consolidation loop is SB-S2); no cross-silo threading (SB-S3); no connector (SB-S4).
+
 ## [0.5.0] - 2026-06-18
 
 ### Added — M0: per-user external data dir (architecture workstream)