feat: add /comms skill — internal communications specialist

[HMAKT99]

Engineering ships 10 PRs/day. The rest of the company finds out next week.

Product doesn't know what features are coming. Sales doesn't know what to demo. New engineers take weeks to ramp up. The information asymmetry grows every sprint.

What /comms does

You:   /comms --weekly

Claude: WEEKLY ENGINEERING UPDATE — Week of Mar 17

        TL;DR: Shipped photo-upload pipeline + 3 bug fixes. Dashboard
        performance issue identified, fix in progress.

        SHIPPED:
        • Photo upload → listing pipeline — sellers can now create
          listings from a single photo (was 5-minute manual process)
        • Fixed: checkout timeout on slow connections
        • Fixed: search results not updating after new listing

        BLOCKED:
        • Dashboard query optimization — need DBA review

        LOOKING AHEAD:
        • Seller analytics dashboard (starts Monday)

Also supports: --incident (3-tier comms), --rfc (translate for non-technical), --allhands (slide prep), --change (change management), --onboard (generate onboarding from codebase).

Only .tmpl committed — bun run gen:skill-docs generates the rest.

Test plan

• .tmpl follows template pipeline
• Registered in gen-skill-docs.ts, skill-check.ts, test files