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.

docker/.env.example

@@ -43,3 +43,16 @@ PORT=auto
 
 # Maximum AI bots per user (default: 5)
 # BOT_MAX_PER_USER=5
+
+# ===========================================
+# OPTIONAL: Shared S3 Storage
+# ===========================================
+# These are only needed if you want app-level shared storage defaults.
+# Most media storage is configured per user inside the app.
+
+# STORAGE_ENDPOINT=
+# STORAGE_REGION=us-east-1
+# STORAGE_BUCKET=
+# STORAGE_ACCESS_KEY=
+# STORAGE_SECRET_KEY=
+# STORAGE_PUBLIC_BASE_URL=