fix(tui): guide bug reports toward failure causes

[cyq1017]

Summary:

• add privacy-first diagnostics guidance to the /feedback bug message
• point users toward environment/tool failure categories before filing
• keep the GitHub template URL unprefilled so prompts, logs, and paths are not copied automatically

Validation:

• cargo test -p codewhale-tui --all-features --locked commands::feedback -- --nocapture
• cargo fmt --all -- --check
• cargo check -p codewhale-tui --all-features --locked
• git diff --check

Refs #2022

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[Hmbown]

Harvested into #2504 as 7c06cf598 for v0.8.50 triage.

I kept this as a narrow #2022 slice: /feedback bug now adds privacy-first diagnostics guidance, keeps the issue URL template-only, and avoids prefilled prompts/logs/paths. Local verification on the harvest branch:

• cargo test -p codewhale-tui --all-features --locked commands::feedback -- --nocapture
• cargo fmt --all -- --check
• git diff --check
• ./scripts/release/check-versions.sh
• cargo clippy -p codewhale-tui --all-targets --all-features --locked -- -D warnings

Thanks @cyq1017.