plan: DIRS-HIERARCHY — walk-up config discovery and configurable source root

[HumanBean17]

Summary

• Adds the execution plan (plans/active/PLAN-DIRS-HIERARCHY.md) for the DIRS-HIERARCHY proposal (propose/active/DIRS-HIERARCHY-PROPOSE.md)
• Single PR plan covering walk-up config discovery, source_root YAML field, precedence chain, CLI/MCP server integration, and 13 named tests
• No ontology bump, no re-index — config discovery only

Scope

• New discover_project_root() function in config.py (walk-up like git)
• Optional source_root field in YAML config
• Two-phase resolution in resolve_operator_config(): find config dir → resolve effective source root
• Updated _project_root() and _resolve_lancedb_uri() in server.py
• init soft warning when parent config detected
• Updated mcp.json.example, README, CONFIGURATION docs

Implements

• propose/active/DIRS-HIERARCHY-PROPOSE.md

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