Define a first-class brownfield adoption path for Fulora

The existing BYO-web-app docs now describe a workable manual path, but the product still lacks a single canonical CLI and config design for teams that already have a frontend. This design spec turns that gap into an explicit brownfield workflow: attach web -> dev -> package.

The document also aligns the proposed workflow with the newer services-first bridge framing and the manifest/hash consistency direction so future implementation work does not reintroduce hidden auto-fix behavior or raw RPC-first ergonomics.

Constraint: Keep the change additive and documentation-only until the attach-web CLI contract is approved
Rejected: Leave brownfield adoption as docs-only composition of existing commands | preserves fragmented DX and weak discoverability
Rejected: Design attach flow around silent regeneration/auto-fix | obscures generation boundaries and weakens deterministic CI behavior
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: Implement attach-web around shared config reuse and explicit consistency checks; do not let later commands drift back to independent heuristics or hidden repair behavior
Tested: Reviewed against existing BYO docs and DX decision doc; git diff --check
Not-tested: markdownlint/doc site build (markdownlint not installed; doc site unaffected because this is an internal spec)

Author: Hongwei-MB