fix(ci): migrate coverage to c8 and fix non-TTY progressBar crash

[jung-thomas]

Problem

Cross-Platform Tests have been failing on main since PR #177 ("refactor: ESM modernization — retire CommonJS-interop shims"). The last green run was #167; every run since — the dependabot bumps and PR #178 — inherited the failure.

The failing step is "Generate coverage report" (npm run coverage:ci), and it fails for two independent reasons:

1. nyc reports 0% coverage under ESM

nyc's instrumenter relied on the CommonJS-interop shims that #177 removed. With native ESM it captures nothing — 0% across all 14k+ statements.

2. The actual exit-1 cause: non-TTY progressBar crash

1) terminal lazy access
     progressBar returns a controller with startItem/itemDone/stop:
   RangeError: Invalid count value: Infinity
     at String.repeat (<anonymous>)
     at redraw (node_modules/terminal-kit/lib/progressBar.js:261:18)

terminal-kit queries the cursor location, which returns Infinity when stdout is not an interactive TTY (CI, piped, redirected), then calls String.repeat(Infinity). Since .nycrc.json had check-coverage: false, this failing test — not the 0% coverage — is what actually exited the step with code 1.

Fix

• Migrate coverage nyc → c8 (V8-native, ESM-aware). .nycrc.json → .c8rc.json with the same include/exclude/thresholds; adds the json reporter so codecov still receives coverage/coverage-final.json. Drops nyc devDependency, adds c8.
• Guard loadRealTerminalSync() in utils/base.js to fall back to the console stub when stdout is not a TTY. This fixes the CI crash and real piped CLI usage (e.g. hana-cli ... > out.log).

Verification (local)

• npm run coverage:ci runs clean — exit 0.
• 555 passing / 0 failing (was 1 failing) — the progressBar test now passes.
• c8 reports real coverage (Statements 15%+) where nyc reported 0%.
• Reproduced the crash directly in NODE_ENV=production non-TTY (piped) — throws before the fix, uses the stub after.
• coverage/coverage-final.json is produced for the codecov upload step.

Notes

• A few .github/instructions/* and rendered docs/ files still mention nyc; those are documentation and don't affect CI. Can update in a docs follow-up if desired.
• Follow-up to PR fix(vscode): propagate container schema for env-var connections #178.