🤖 feat: flatten tool hook env vars

[ammar-agent]

Summary

Add shell-friendly flattened tool hook env vars (MUX_TOOL_INPUT_<…> / MUX_TOOL_RESULT_<…>) so hooks can access common fields without JSON parsing.

Background

Hooks are frequently authored in bash, and parsing MUX_TOOL_INPUT with jq/Python is noisy. We still keep the raw JSON env vars + *_PATH files for full fidelity and backwards compatibility.

Implementation

• Introduce shared flattening + naming helper (src/common/utils/tools/toolHookEnv.ts) used by both runtime and docs generation.
• Populate flattened env vars for legacy tool_hook and new tool_pre/tool_post paths.
• Avoid env bloat by capping emitted vars/array length and omitting oversized values (rely on *_PATH).
• Auto-generate per-tool env var appendix in docs/hooks/tools.mdx from TOOL_DEFINITIONS.
• Update examples to use flattened vars instead of jq.

Validation

• bun test src/common/utils/tools/toolHookEnv.test.ts
• bun test src/node/services/hooks.test.ts
• bun scripts/gen_docs.ts
• make static-check

Risks

• Environment size/SSH command length: mitigated via conservative caps + omission of oversized values (fallback to *_PATH).

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