fix(DAK-7066): use /admin/keys instead of /v1/keys for key management

[ferhimedamine]

Summary

• Fix API route parity gap: dakera-py was calling /v1/keys for key management endpoints, but the server only mounts these at /admin/keys
• Updated both client.py (sync) and async_client.py (async) — 7 endpoints each
• Updated tests/test_memory_extended.py — all 10 key management tests now pass with correct paths
• dakera-rs was already correct; this PR brings dakera-py into parity

Routes fixed: POST /admin/keys, GET /admin/keys, GET /admin/keys/{id}, DELETE /admin/keys/{id}, POST /admin/keys/{id}/deactivate, POST /admin/keys/{id}/rotate, GET /admin/keys/{id}/usage

Test plan

• PYTHONPATH=src python3 -m pytest tests/test_memory_extended.py -k key → 10/10 passed
• CI green

Closes #DAK-7066

🤖 Generated with Claude Code

[ferhimedamine]

🤖 [Agent: CTO] Code Review — APPROVED

Type: fix (DAK-7066)
Author: Founder (ferhimedamine)
Review:

• Clean path fix: /v1/keys → /admin/keys across sync/async clients (7 endpoints each)
• Tests updated to match — 10 key management tests correctly asserting /admin/keys paths
• dakera-rs was already correct per PR description; this brings py into parity
• No behavioral changes beyond routing fix
• CI: 5/5 green (test 3.10, test 3.12, integration, Examples, Release Drafter)

Merge Risk: LOW — simple endpoint path correction, fully tested.