docs(dev): add adapter authoring knowledge, guidelines, and guides

[BeArchiTek]

Problem

The repo recently gained the agentic dev/ structure (constitution, ADR, and stub
knowledge/guidelines/guides READMEs), but the buckets had no content. There was no
single place explaining how to write an adapter — the architecture, the rules, and the
procedure — and AGENTS.md's terse 5-step "Adding a New Adapter" list was the only guidance.

Solution

Populate the three dev/ buckets with adapter-focused documentation for humans and agents,
following the infrahub dev/ conventions (descriptive knowledge, prescriptive guidelines,
procedural guides; hub-and-spoke cross-linking):

• knowledge/ — sync architecture, adapter anatomy (the DiffSyncMixin / DiffSyncModelMixin
  contract), schema mapping, and incremental sync & cache.
• guidelines/ — rules for writing and testing an adapter.
• guides/ — step-by-step procedures for adding and testing an adapter.

AGENTS.md's "Adding a New Adapter" section is trimmed to a pointer at
dev/guides/adding-an-adapter.md, so the canonical procedure lives in one place and does not
drift.

Content is grounded in the actual code (the mixin contract, the netbox adapter, the
genericrestapi → peeringmanager base pattern, the examples/custom_adapter worked example,
and the existing tests/adapters/ patterns). No source-code changes and no user-visible CLI
or config changes. markdownlint is clean and all relative cross-links resolve.

Before / after — AGENTS.md "Adding a New Adapter"

• Before: a 5-step inline list.
• After: a pointer to dev/guides/adding-an-adapter.md plus links to the dev/ reference
  set, keeping the read-only-list/diff-before-sync rule inline.

Summary by CodeRabbit

• Documentation
  • Expanded the adapter documentation with new, structured guides and reference pages.
  • Added end-to-end instructions for building adapters, writing tests, and understanding adapter structure, sync architecture, schema mapping, and incremental/cached sync behavior.
  • Improved documentation navigation with clearer indexes and links across adapter-related materials.
  • Updated existing adapter setup guidance to point to the full guide while keeping key safety rules intact.

[cloudflare-workers-and-pages]

Deploying infrahub-sync with    Cloudflare Pages

Latest commit:	c4c25f3
Status:	✅  Deploy successful!
Preview URL:	https://99a029ba.infrahub-sync.pages.dev
Branch Preview URL:	https://docs-dev-adapter-guides.infrahub-sync.pages.dev

View logs

[coderabbitai]

Walkthrough

This PR adds a complete developer documentation set for infrahub-sync adapters. New knowledge pages cover sync architecture, adapter anatomy (DiffSyncMixin and DiffSyncModelMixin contracts), schema mapping configuration, and incremental sync with cursor tiers and caching. New guideline documents define prescriptive rules for writing and testing adapters. New step-by-step guides walk through adding an adapter end-to-end and writing adapter tests. All existing navigation entry points—dev/knowledge/README.md, dev/guidelines/README.md, dev/guides/README.md, and AGENTS.md—are updated with structured indexes linking to the new content.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: new adapter-authoring documentation under dev knowledge, guidelines, and guides.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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