Add Redis infrastructure and state management

[RafaelPo]

Summary

PR 2 of 5 in the HTTP transport split (follows #179).

• redis_utils.py: Redis client factory with Sentinel support, exponential backoff retry, health checks, and build_key() helper with colon-sanitization to prevent key injection
• state.py: ServerState dataclass with Redis-backed storage for task tokens, poll tokens, result metadata, page previews, and CSV results — all with TTLs, no in-memory dicts, fully multi-pod safe
• Test infrastructure: Real Redis tests via redis-server on port 16379 (session-scoped fixture, flushed between tests), plus CI redis-server installation step
• Dependency: Added redis>=5.0.0 to pyproject.toml

Multi-pod safety

All mutable shared state goes through Redis — no module-level dicts or process-local caches. Sentinel support is included for production HA. Connections use retry with exponential backoff and periodic health checks.

Test plan

• test_redis_utils.py — build_key helper and create_redis_client factory (direct + Sentinel modes)
• test_state_redis.py — Round-trip tests for all Redis-backed ServerState methods (task tokens, poll tokens, result meta, page previews) plus graceful degradation when Redis is None
• All 60 existing tests pass, pre-commit hooks (format, lint, typecheck) pass

🤖 Generated with Claude Code

[sentry]

Bug: The create_redis_client function is defined but never called in the production code, leaving the Redis integration feature incomplete and non-operational.
_{Severity: HIGH}

Suggested Fix

Integrate the create_redis_client function into the application's initialization logic. This likely involves calling it when the ServerState is created and using its return value to populate the store field if Redis is configured.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: everyrow-mcp/src/everyrow_mcp/redis_utils.py#L42

Potential issue: The function `create_redis_client` in `redis_utils.py` is defined to
establish a connection to a Redis instance, including support for Redis Sentinel.
However, this function is never called anywhere in the production application code. Its
only usage is within the test suite. As a result, even if Redis Sentinel endpoints are
configured, the application will not attempt to connect to Redis, rendering the feature
incomplete and non-functional.

_{Did we get this right? 👍 / 👎 to inform future reviews.}