feat(discord): add configurable tool display

[chihkang]

Summary

• add reactions.tool_display with full, compact, and none modes
• render compact Discord tool lines without full command arguments while keeping full for debugging
• document the new setting in config.toml.example, README.md, and the Helm chart values/configmap

Testing

• cargo test
• rustfmt --edition 2021 --check src/config.rs src/discord.rs
• git diff --check

Closes #216

[thepagent]

Heads up — #253 just merged, which refactored compose_display() to add streaming-mode tool collapsing. This PR will have merge conflicts in src/discord.rs since both modify the same function.

When rebasing, please note:

• compose_display() now takes a third streaming: bool parameter
• Tool collapsing (threshold-based) is already handled for the streaming path
• Your full/compact/none modes could layer on top nicely — compact could leverage the existing collapse logic, and none could skip tool rendering entirely

Please rebase on main and resolve conflicts. Happy to re-review after! 🙏

[github-actions]

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[chihkang]

Rebased onto main and resolved the compose_display() conflicts.

I kept the new streaming collapse behavior from #253 and layered the tool_display modes on top of it:

• full preserves full tool titles
• compact reuses the existing streaming collapse behavior while rendering compact labels for individual tool lines
• none skips tool rendering entirely

I also synced Cargo.lock to the current 0.7.5 package version after rebasing.

Verification:

• cargo test
• rustfmt --edition 2021 --check src/config.rs src/discord.rs
• git diff --check