Follow-up to #236. A small corrective delta stacked on top of that PR's generator hardening; it will be rebased down to only the delta once #236 lands.

This delta was blind-planned: two independent planners designed the generator fix from a solution-stripped problem statement (without seeing #236), and both independently flagged the three gaps below that #236 left open.

What this changes in skills/linear-cli/scripts/generate-docs.ts

• deno fmt failure is now fatal instead of a logged warning. The format step runs after the docs are written, so a silent failure would leave unformatted docs that break deno fmt --check in CI once committed.
• The top-level error boundary prints a concise message (Error: <message>) instead of the raw error object and its stack trace, on every abort path (missing binary, failed help fetch, fmt failure).
• SKILL.md is rendered from its template before writeReferences prunes any stale docs, so a missing or broken template aborts before the references directory is touched — extending refactor(skill-docs): harden generator and make output deterministic #236's own "write before prune / abort before write" invariant to the template read.

None of these change the generated doc output — they are pure control-flow/error-handling. deno task generate-skill-docs remains idempotent.

Note: while this branch is a draft it still contains #236's commits. The first CI run therefore diffs the superset (#236 + this delta) against main; after #236 merges, this will be rebased to only the delta and marked ready.