feat: multi-instance support — agent_name and user_name configurable

All hardcoded "Inara"/"Scott" strings replaced with settings.agent_name
and settings.user_name, read from .env at startup:

- config.py: AGENT_NAME and USER_NAME settings (defaults: Inara / Scott)
- llm_client.py: conversation labels in prompt builder
- session_logger.py: **Name:** labels in session log markdown
- memory_distiller.py: distillation system prompts (mid + long)
- routers/nextcloud_talk.py: @mention prefix strip
- routers/google_chat.py: greeting message

Second instance scaffolding:
- holly/: identity directory with placeholder files (USER_NAME=Holly,
  AGENT_NAME to be chosen by Holly)
- cortex/.env.holly: config for Holly's instance on port 8001
- cortex-holly.service: systemd unit for the second instance

No behavioural change to the Inara/Scott instance — defaults unchanged.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cortex/.env.holly

@@ -0,0 +1,36 @@
+# Holly instance .env
+# Copy secrets from cortex/.env (API keys, NC Talk secret etc.)
+# then customise the identity settings below.
+
+# TODO: Set AGENT_NAME to whatever name Holly chooses for her agent
+AGENT_NAME=TBD
+USER_NAME=Holly
+
+PORT=8001
+HOST=0.0.0.0
+
+INARA_DIR=/home/scott/agents_sync/projects/Cortex_and_Inara_dev/holly
+SESSIONS_DIR=/home/scott/agents_sync/projects/Cortex_and_Inara_dev/holly/sessions
+
+DEFAULT_MODEL=claude-sonnet-4-6
+DEFAULT_TIER=2
+
+# ── Copy these from cortex/.env ──────────────────────────────────────────────
+GEMINI_API_KEY=
+AE_API_URL=https://dev-api.oneskyit.com
+AE_API_KEY=
+AE_ACCOUNT_ID=
+
+NEXTCLOUD_URL=https://cloud.dgrzone.com
+NEXTCLOUD_TALK_BOT_SECRET=
+
+# Per-backend timeouts
+TIMEOUT_CLAUDE=60
+TIMEOUT_GEMINI=120
+TIMEOUT_LOCAL=300
+
+SCHEDULER_TIMEZONE=America/New_York
+AUTO_DISTILL=true
+AUTO_DISTILL_SHORT=true
+AUTO_DISTILL_MID=true
+AUTO_DISTILL_LONG=false