Migrate v1 docs into v2-compliant documentation set (rewrite concepts into new topic-based docs)

### Background
The legacy Beckn Protocol v1 repository (`beckn/protocol-specifications`) contains a set of foundational docs (network policy, payments, communication, policy admin, error codes, signing, XInput, rating/reputation, tags, etc.) maintained across `main` and `draft` branches.

This repository is the v2.0.0 (RC) specification. We need a **comprehensive conceptual migration** of the v1 documentation into a **new v2-compliant documentation information architecture**, not a file copy.

**Important:** We will **not** import the original v1 markdown files into this repo. Instead, we will rewrite and restructure the content so it aligns with v2 concepts, entities, and architecture.

### Goals
- Rewrite the concepts in the v1 docs into a coherent, v2-aligned documentation set under `docs/`.
- Adopt **topic-based slugs / directories** (e.g., `docs/security/signing.md`, `docs/network/policy.md`) rather than BECKN-### filenames.
- Optionally preserve v1 BECKN doc IDs in **front-matter** and/or "Sources" section for traceability.
- Produce explicit **deprecation / superseded** notes (in the new docs) describing how v1 concepts map to v2.

### Source material to migrate (v1 repo)
Repo: https://github.com/beckn/protocol-specifications
Branches to use as inputs: `main` + `draft`

Primary source directory:
- `docs/`
- `BECKN-001-Layering-Network-Policy-Draft-01.md`
- `BECKN-002-Payments-On-Beckn-Enabled-Networks.md`
- `BECKN-003-Beckn-Protocol-Communication-Draft-01.md`
- `BECKN-004-Policy-Administration-On-Beckn-Enabled-Networks.md`
- `BECKN-005-Error-Codes-Draft-01.md`
- `BECKN-006-Signing-Beckn-APIs-In-HTTP-Draft-01.md`
- `BECKN-007-The-XInput-Schema.md`
- `BECKN-008-Rating-and-Reputation-on-Beckn-Protocol.md`
- `BECKN-009-Tags-the-Edge-of-Beckn.md`
- plus `draft` branch additions:
- `BECKN-010-Keyword-Definitions-for-Technical-Specifications.md`
- `BECKN-011-Search-Provider-Draft-01.md`
- `docs/images/` (for conceptual reference only; reuse only if needed for v2 docs)

### Non-goals
- Do not copy v1 markdown files verbatim into `docs/v1` or elsewhere.
- Do not keep v1 numbering as the primary navigation scheme.

### Deliverables
1. **New v2 documentation IA** under `docs/` using topic-based paths.
2. A **mapping index** that provides traceability:
- v1 doc → new v2 doc(s) (section-level mapping where useful)
3. Updated `docs/README.md` (currently TBD) as a proper entrypoint for the new docs tree.
4. Each migrated doc includes:
- "What changed from v1 → v2" section
- Explicit references to relevant v2 artifacts in this repo (schema packs, OpenAPI, JSON-LD contexts)

### Proposed target IA (initial proposal)
This is a starting point; refine during implementation.

- `docs/architecture/`
- `overview.md` (how v2 is organized: core + schema packs, JSON-LD, actors)
- `layering-and-network-policy.md` (from BECKN-001)
- `docs/network/`
- `policy-administration.md` (from BECKN-004)
- `registry-and-discovery.md` (v1→v2: registry changes + BG→CDS)
- `docs/security/`
- `signing-http-apis.md` (from BECKN-006, updated for v2 envelopes and flows)
- `docs/api/`
- `communication-patterns.md` (from BECKN-003; async patterns, callbacks, error handling)
- `search-and-discovery.md` (from BECKN-011 but rewritten for v2 CDS/discover model)
- `docs/transactions/`
- `payments.md` (from BECKN-002; updated to v2 Payment/Settlement types)
- `docs/reference/`
- `error-codes.md` (from BECKN-005; align to v2 error model)
- `keywords-and-terminology.md` (from BECKN-010)
- `docs/extensibility/`
- `xinput.md` (from BECKN-007; ensure it makes sense in v2 context)
- `tags.md` (from BECKN-009; v2 tagging + JSON-LD considerations)
- `docs/trust/`
- `rating-and-reputation.md` (from BECKN-008)

### Work plan / tasks
#### Phase 0 — Repo baselining
- [ ] Define doc template (front-matter keys, headings, "v1→v2 changes" section)
- [ ] Define folder conventions for `docs/` (topic-based)

#### Phase 1 — Source analysis + mapping
- [ ] Extract an outline (TOC) of each v1 doc from `main` and `draft`
- [ ] Produce a mapping matrix (v1 doc sections → target v2 doc paths)
- [ ] Identify v1 concepts that are obsolete in v2 (e.g., BG vs CDS) and record rewrite decisions

#### Phase 2 — Rewrite & author v2-compliant docs
- [ ] Create new markdown docs under the target folders
- [ ] Rewrite content in v2 terminology and architecture
- JSON-LD entities, schema packs, core vs domain attributes
- CDS replaces BG, DeDi-compliant registry replaces legacy registry APIs
- v2 API/flow naming and surfaces
- [ ] Add "Supersedes v1" / "Deprecation notes" section in each doc
- [ ] Add cross-links between docs (navigation)

#### Phase 3 — Review & consolidation
- [ ] Ensure no duplicated/conflicting definitions across docs
- [ ] Validate that the docs reflect what exists in this repo (e.g., `api/beckn.yaml`, `schema/core/v2/**`)
- [ ] Add/refresh `docs/README.md` as a complete docs index

### Acceptance criteria
- A full set of topic-based v2 docs exists in `docs/` covering all concepts from v1 docs.
- For every v1 doc in `beckn/protocol-specifications/docs/` (main + draft), there is:
- at least one corresponding v2 doc, and
- a mapping entry that points to where the concepts landed.
- The resulting v2 docs do **not** reference deprecated v1-only constructs without explicitly describing the v2 replacement.
- `docs/README.md` is no longer "TBD" and provides a navigable index into the docs tree.

### Notes / risks
- Some v1 docs may describe constructs that are fundamentally changed in v2; these sections should be rewritten as "historical context" only if strictly necessary, otherwise replaced with v2-native guidance.
- We may need multiple reviewers (protocol + schema + API) because this is semantic migration, not mechanical.