Fog referral gate in /nxs.epic

[sameera]

As a delivery lead, I want /nxs.epic to stop when an intent's functional goals cannot be stated sharply and refer me to /nxs.discover, so that underspecified initiatives are no longer answered with work-shaped stubs.

Acceptance Criteria

• Given an intent, when /nxs.epic reaches its right-size phase, then the sharpness test runs before sizing. The test is the stub shape itself: can each functional goal be stated as a one-line goal, with a small estimate, and with candidate story titles? If decomposition cannot produce that shape, the intent is underspecified rather than merely oversized.
• Given an intent whose functional goals cannot be stated sharply, then /nxs.epic stops before sizing (house MANDATORY-STOP and AskUserQuestion convention) and presents /nxs.discover as the recommended path, filing nothing.
• Given that stop, then an explicit override is offered that falls through to the existing sizing path. Nothing is filed before the lead makes a choice. The sharpness call is a judgement the lead owns, so a false positive stays recoverable.
• Given an oversized but clearly specified intent, then the existing L, XL, and XXL path is unchanged and the split-to-stubs offer still fires.
• Given a sharp, right-sized intent, then the gate adds no new interaction and planning proceeds as today.
• Given an entry mode other than intent — a stub being promoted by issue number, or a discovery being consumed — then the gate does not fire. A promoted stub was already discovered, and a consumed discovery is the output of the very thing the gate refers people to, so firing there would deadlock work discovery itself produced.

Notes

The gate distinguishes underspecified (foggy, refer to discovery) from oversized (big but clear, existing decomposition path). It lives inside the right-size phase rather than as a phase of its own: that shape is already the output the decomposition step must produce, so the test adds no new machinery, and living inside the sizing phase inherits the skip-in-promotion rule for free.

This story and #231 are the two changes this epic makes to /nxs.epic. Neither adds a phase.