Add installer, CI, ARM build and test updates

Introduce a one‑line Docker installer and environment examples, add CI and docker validation workflows, and update docs and tests.

Key changes:
- Add docker/install.sh installer that bootstraps /opt/synapsis, downloads compose files, optionally installs Docker, and generates secrets.
- Add top-level .env.example and docker/.env.example entries for shared storage and local development.
- Add GitHub Actions CI (ci.yml) with type checks, targeted vitest runs, build and docker-compose validation.
- Update existing docker workflow to set up QEMU and build multi‑arch images (amd64, arm64).
- Update README and docker/README to use the installer, point to the new repo, adjust local setup instructions, and note shared S3 env vars.
- Update docker-compose comments and include shared S3 env variables and defaults.
- Update .gitignore to ignore site-work mirrors.
- Tests: expand supported bot source types (add brave_news, youtube), increase POST_MAX_LENGTH from 400 to 600, add minimal user handle in mention handler tests, and add mocks & test adjustments in scheduler tests to keep them unit-scoped.

These changes simplify installation, add CI coverage (including Docker config validation), enable multi‑arch builds, and align tests with expanded bot source/validation behavior.

.env.example

@@ -0,0 +1,32 @@
+# Synapsis local development environment
+# Copy to .env and adjust values for your machine.
+
+# Required: local database
+DATABASE_URL=postgres://postgres:postgres@localhost:5432/synapsis
+
+# Required: used for sessions, node key encryption, and bot API key encryption
+AUTH_SECRET=replace-with-a-long-random-secret
+
+# Required for admin access. Register with one of these emails locally.
+ADMIN_EMAILS=admin@example.com
+
+# Recommended: local node identity
+NEXT_PUBLIC_NODE_DOMAIN=localhost:3000
+NEXT_PUBLIC_APP_URL=http://localhost:3000
+
+# Optional: node metadata shown before a node record exists in the database
+# NEXT_PUBLIC_NODE_NAME=Synapsis Local
+# NEXT_PUBLIC_NODE_DESCRIPTION=Local development node
+# NEXT_PUBLIC_ACCENT_COLOR=#FFFFFF
+
+# Optional: bot limits
+# BOT_MAX_PER_USER=5
+
+# Optional: app-level storage fallback. Most media storage is user-owned and can be
+# configured in the app, so these are only needed if you want a shared default.
+# STORAGE_ENDPOINT=
+# STORAGE_REGION=
+# STORAGE_BUCKET=
+# STORAGE_ACCESS_KEY=
+# STORAGE_SECRET_KEY=
+# STORAGE_PUBLIC_BASE_URL=