feat(inference): add tool schema translation layer

[Svagtlys]

Closes #78

Description

Translate MCP tool inventories (ToolInfo.input_schema) into OpenAI-compatible function tool definitions carried on CompletionRequest.tools, with mcp__<server>__<tool> dedupe and a reverse-routing map. Request-side only: response-side tool-call parsing lands with the agent loop.

Implementation

• ToolDefinition model + CompletionRequest.tools field in the inference vocabulary
• OpenAIAdapter._chat_kwargs wraps definitions into the {"type": "function", ...} wire envelope (absent when none/empty)
• New pure octave.tools package: translate_tools() converts ServerToolInventory fleets into ProviderToolset (defs + routes), sanitizing/truncating exposed names to the OpenAI charset (^[a-zA-Z0-9_-]{1,64}$) and raising ToolNameCollisionError on collisions
• JSON Schema bodies pass through verbatim minus $schema, deep-copied so inputs are never mutated
• Neither octave.mcp nor octave.inference imports the other; SDK quarantine guarded by an AST hygiene test

References

• Design doc: .agents/specs/2026-09-22-tool-schema-translation-design.md
• Implementation plan: .agents/specs/2026-09-22-tool-schema-translation.md

Checklist

• Tests passing (277 passed)
• Lint clean (ruff + mypy strict)
• Frontend builds (not applicable — no frontend changes)