Execute Progressive Disclosure Migration for AGENTS.md

Context As established in Epic #11411, AGENTS.md is currently ~27.6KB, which breaches the combined 24KB Antigravity limit when combined with other memory files, causing severe truncation of the Escalation Ladder and workflow skills.

The Problem We must adapt our core L1 anchor to survive the strict byte limit by heavily applying Progressive Disclosure (Map vs. World Atlas).

The Architectural Reality The bottom half of AGENTS.md currently contains massive tables for Workflow Skills, edge-case triggers, and sunset protocols. These do not need to be loaded on every single turn; they can be loaded dynamically when their triggers fire.

The Fix Shave ~3.7KB off AGENTS.md by migrating the heavy Workflow Skills table and other granular details into a new Atlas file (e.g., .agents/skills/workflow-routing.md or similar).

Acceptance Criteria

• AGENTS.md size is reduced to comply with its allocation in the new byte-budget table.
• The heavy Workflow Skills table is extracted to a localized .agents/skills/ Atlas file.
• AGENTS.md retains the critical L1 Identity Anchor and pointers to the extracted Atlas files (No duplicate-body rule enforced).
• ANTIGRAVITY_RULES.md is scrubbed of cross-harness rules and strictly retains Antigravity-specific survival mechanics.

Out of Scope

• CI mechanical guard implementation (handled in Sub 1).

Related

• Parent Epic: #11411

Origin Session ID: 188acb85-b41e-435c-94ee-0cc9944d4c97