Add ecosystem-mode compose overrides for fluent-ai integration

[JEdward7777]

Summary

Adds ecosystem-mode Compose overrides so the fluent-platform stack wires up correctly when running fluent-api (Node backend) together with fluent-ai (the new Python AI backend) on the shared Compose network.

Changes to compose.yaml

• Mount fluent-api/scripts into the api container (read-only), alongside the existing source mounts.
• FLUENT_AI_URL: http://ai:8200 on the api service — reach fluent-ai by its service name on the shared network, overriding the standalone fluent-api/.env value (http://localhost:8200). FLUENT_AI_KEY is intentionally not overridden so the caller key stays in lockstep with fluent-ai's ai_api_keys seed.
• MIGRATIONS_DATABASE_URL override for the ai service to use the migrations:postgres credentials that the platform DB's db/init/init-db.sql actually assigns. The standalone fluent-ai/.env default (migrations:password) causes an asyncpg InvalidPasswordError on the platform DB and the ai container exits at the Alembic step.
• UV_CACHE_DIR: /tmp/.uv-cache instead of /app/.cache/uv, which lands on the noexec tmpfs and breaks uv cache init ("Permission denied"). Also bumps the /tmp tmpfs from 64m to 256m to fit the cache.

⚠️ Dependency note

This PR is a prerequisite for the corresponding fluent-api PR's tests to run cleanly. Without these Compose overrides, the connection between fluent-api and fluent-ai fails to authenticate, so the fluent-api integration tests cannot pass.

[JEdward7777]

Paired with fluent-api PR eten-tech-foundation/fluent-api#181 — this compose change is the prerequisite that lets fluent-api authenticate against fluent-ai (and brings the ai container up from a clean slate) so that PR's integration runs cleanly.