Add ToolRegistry with static tool definitions

[bug-ops]

Parent: #239 (Phase A)

Summary

Introduce ToolRegistry holding typed ToolDef structs for all built-in tools.

Changes

• crates/zeph-tools/src/registry.rs (new): ToolDef, ParamDef, ParamType, ToolRegistry
• Static definitions for 7 tools: bash, read, edit, write, glob, grep, web_scrape
• Unit tests for registry

Acceptance criteria

• ToolRegistry holds definitions for all 7 tools
• Each ToolDef has id, description, typed parameters
• Unit tests pass