Remove deprecated agent and prompt files; add new architecture, contract, and feature documentation for Reader API

SKILLS.md

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+# Shared Development Skills (Reader Suite)
+
+Tai lieu mo ta bo skill de phat trien thong nhat giua web/app/api.
+
+## skill: feature-parity-check
+- Muc dich: so sanh 1 feature giua web va mobile theo cung API contract.
+- Input: ten feature, endpoint list, expected UX behavior.
+- Output: parity report (done/missing/risk) cho 3 repo.
+
+## skill: api-contract-guard
+- Muc dich: review thay doi API de tranh breaking web/mobile.
+- Input: diff endpoint, request/response schema, auth requirement.
+- Output: compatibility checklist + migration huong dan.
+
+## skill: auth-flow-verifier
+- Muc dich: verify luong dang nhap web cookie va mobile JWT map cung identity.
+- Input: login flow, token/session behavior, protected endpoints.
+- Output: matrix pass/fail + fix recommendation.
+
+## skill: release-readiness
+- Muc dich: chuan bi release dong bo 3 repo.
+- Input: danh sach thay doi theo repo.
+- Output: rollout order, smoke-test list, rollback note.