docs(releases): lead v15 with outcome-oriented highlights; move technical detail down

Restructure per release review: the page now opens with plain-language
Highlights for 15.0.0 and 15.1.0 (what you can do now, not how it's built),
followed by the detail sections in feature-first order (features → Console →
breaking/migration → behavior → hardening). No content removed — breaking
changes and migrations keep their full text, they just stop leading the page.
Frontmatter and index descriptions reworded to outcomes.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: os-zhuang

content/docs/releases/index.mdx

@@ -18,7 +18,7 @@ migration steps, then covers new capabilities and notable fixes.
 
 ## Versions
 
-- [v15.0.0](/docs/releases/v15) — Authorization kernel chain (ADR-0095): tenant isolation as an always-first Layer 0, a capability-derived posture ladder, record-grained access explanation; strict view/page schemas (ADR-0089); the objectui 14.0 Console major (docked ChatDock, Gantt batch). The 15.1 line adds a write-path security hardening sweep, attachments v1, declarative connectors (ADR-0096/0097), dashboard-level filters, and pinyin search (current series: 15.1.0).
+- [v15.0.0](/docs/releases/v15) — Explain record access layer by layer, a docked AI workspace in the Console, project-ready Gantt charts, and phone sign-in; 15.1 adds permission-following attachments, no-code third-party connectors, dashboard-wide filters, pinyin search, and whole-record inline editing — with materially safer multi-tenant and write-path defaults (current series: 15.1.0).
 - [v14.0.0](/docs/releases/v14) — ADR-0090 vocabulary convergence completed, object `enable.*` flags become real gates, admin user management, phone/SMS auth, book-audience enforcement, data-lifecycle contract, and effective-dated grants (final release: 14.8.0).
 - [v13.0.0](/docs/releases/v13) — Permission Model v2 (ADR-0090): Roles and Profiles converge on Positions, custom objects default to private, plus an explain engine, delegated administration, and self-serve MCP OAuth.
 - [v12.0.0](/docs/releases/v12) — Anonymous data access denied by default (ADR-0056 D2), adaptive record surfaces, an enforced protocol-version handshake, and build-gating author-time lints.