Consolidate nf-bin/ and nf/bin/ providers.json paths #167

Context

bin/install.js maintains two parallel installed locations for providers data:

• ~/.claude/nf-bin/providers.json — written by mergeProvidersJson with user-extras merge semantics
• ~/.claude/nf/bin/providers.json — mirror, mostly populated by ensureMcpSlotsFromProviders and referenced by mcpServers via UNIFIED_PROVIDERS_CONFIG

The split is the root cause of multiple bugs shipped on 2026-05-12/13:

• /nf:link-daintree writes slash, mergeProvidersJson writes dash → preset-cloned slots invisible to install (fix(link-daintree): make fan-out idempotent (canonical vanilla + preserve metadata on install) #159)
• quorum-preflight.cjs + call-quorum-slot.cjs read dash, so quorum dispatch silently omits Daintree slots (fix(quorum): prefer slash-path providers.json so Daintree slots are visible #165)
• Mirror step copies dash → slash only when slash doesn't exist (!fs.existsSync(destFile)), so the slash path lags behind whenever the slot was previously created via fan-out

Comments throughout the codebase note LLMs frequently guess one path or the other, suggesting the dual-path architecture is a recurring confusion.

Proposed solution

Pick one canonical path and migrate. Suggested: keep ~/.claude/nf-bin/ (matches the manifest pattern shared by other installed bin dirs) and turn ~/.claude/nf/bin/ into a symlink for backwards-compatible reads. Update all mcpServers.*.env.UNIFIED_PROVIDERS_CONFIG entries during install to point at the canonical path.

Acceptance criteria

• Only one canonical providers.json location on disk
• Existing ~/.claude.json mcpServers entries are migrated to point at the canonical path
• /nf:link-daintree, install.js, quorum-preflight.cjs, call-quorum-slot.cjs, unified-mcp-server.mjs all read/write the same location
• Tests added to prevent the dual-path resurfacing