#11980: CLI: add external message lint + warn on tables/mentions

Adds external message linter + CLI lint warnings; includes table + mass-mention warnings. Tested: bun scripts/external-message-lint.ts --help; bun ... --json --file BOOTSTRAP.md <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR adds a new external message linter (`scripts/external-message-lint.ts`) and wires message-formatting warnings into the CLI message helpers, plus new snapshot/debug scripts and documentation updates around “pasteable” formatting (no headings/tables/fences, limit questions/lines). Main correctness issues are confined to the new linter CLI parsing and a regression in the repo’s pre-commit hook behavior introduced in the same commit set. <h3>Confidence Score: 2/5</h3> - This PR has a couple of must-fix issues that can break developer workflows and mis-handle CLI input. - Score reflects (1) a pre-commit hook change that removes oxlint auto-fixes and may pass an invalid flag through to oxfmt, potentially blocking commits, and (2) `external-message-lint` treating the next flag as a file path after `--file`, producing confusing failures. Other changes look additive and low-risk. - git-hooks/pre-commit, scripts/external-message-lint.ts <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->