#23770: docs: fix broken URL, inconsistent casing, and hyphenation

## Summary - **twitch.md**: Remove stray `%20` from StreamWeasels URL (canonical URL has no space) - **msteams.md**: Replace one-off `Explainable:` label with `Why:` to match codebase convention - **gateway/troubleshooting.md**: Capitalize "Control UI" (180+ uses vs 2 lowercase), hyphenate "symptom-based" and "channel-specific" (14+ hyphenated uses elsewhere) - **channels/troubleshooting.md**: Hyphenate "channel-level", "per-channel", and "channel-specific" to match established convention ## Test plan - [x] Verify the docs render correctly on Mintlify - [x] Verify the fixed Twitch URL resolves correctly <!-- greptile_comment --> <h3>Greptile Summary</h3> This PR fixes documentation consistency issues across four files: - **twitch.md**: Removes stray `%20` from StreamWeasels URL (the canonical URL uses hyphens, not spaces) - **msteams.md**: Replaces one-off `Explainable:` label with `Why:` to match the established convention used elsewhere (3 other occurrences in docs) - **gateway/troubleshooting.md**: Capitalizes "Control UI" (150+ capitalized uses vs 2 lowercase), hyphenates "symptom-based" (consistent with the only other occurrence) - **channels/troubleshooting.md**: Hyphenates "channel-level", "per-channel", and "channel-specific" to match established pattern (14+ hyphenated uses elsewhere) All changes improve consistency with existing codebase conventions without altering any functional content. <h3>Confidence Score: 5/5</h3> - This PR is completely safe to merge with zero risk - All changes are purely cosmetic documentation fixes (URL typo, capitalization, hyphenation) that improve consistency with established codebase conventions. No functional code, logic, or behavior is affected. The changes have been verified against the codebase to confirm they match existing patterns (e.g., "Control UI" appears 150+ times capitalized, "channel-level" and "per-channel" are consistently hyphenated elsewhere). - No files require special attention _{Last reviewed commit: fc08fab} <!-- greptile_other_comments_section --> _{(5/5) You can turn off certain types of comments like style [here](https://app.greptile.com/review/github)!} <!-- /greptile_comment -->