[P2 documentation] Correct SDK, configuration, schema, and version drift

[jp-cruz]

Problem

Several public examples and operational claims do not match the implementation, increasing integration and incident-response risk.

Examples

• README SDK snippets use tool_name, tool_input, and agent_state, while the SDK requires tool_id, action, args, agent_id, run_id, and sequence_so_far.
• README documents GUARDIAN_DB_*, while the service reads POSTGRES_*.
• Application responses advertise version 4.0.0, while package metadata is 0.1.1.
• Database setup says Guardian needs two tables, while init.sql creates five.
• Health and authentication response semantics are described inconsistently.

Acceptance criteria

• Every README SDK example runs as a tested doctest or executable documentation test.
• Environment-variable names come from one settings definition and match README, Compose, and .env.example.
• Package, CLI, API, health, and documentation versions derive from one source.
• Database prerequisites and upgrade behavior match the actual schema.
• Endpoint auth and status-code behavior are documented exactly.
• CI fails when executable examples or generated configuration reference drift.