docs: fork sync methodology + deviation register (#52)

* docs: add fork sync and upgrade methodology

Codifies how @vacbo/oh-my-opencode stays synced with upstream
code-yeongyu/oh-my-openagent, how fork-only fixes land, how we guard
against AI slop via the existing analyzer rubric, and when we publish
npm releases.

The document describes what is already automated (upstream-tag-watcher +
upstream-analyzer + publish.yml) and the six manual steps the maintainer
still owns after the analyzer opens draft PRs.

Includes a correction: DeepWiki (upstream PR #868) is a README badge,
not an MCP server or plugin feature.

* docs: add fork deviation register for the 43 fork-only commits

Categorizes every commit on dev that is not on upstream/dev as of fork
HEAD 5cd78886 into six groups: analyzer-infra (14), sync-cherrypick
(11), scoped-package (8), fork-only-fix (5), ci-hardening (3), and
release-bot (2). Total reconciles against git log upstream/dev..dev.

Referenced by docs/SYNC_METHODOLOGY.md section 7. Every new fork-only
PR must add a row before merge.

* docs: reframe methodology section 0 around the read-the-diff principle

The prior section 0 was titled 'DeepWiki is not an MCP' and centered on
that single upstream PR. The rule underneath — read the diff, not the
title — is broader and more useful. Retitled accordingly; DeepWiki PR
#868 demoted to the worked example that illustrates the rule. Closes the
loop with section 6 where the classifier applies the same discipline to
every commit in the analysis window.