refactor: migrate all 7 CLIs onto @deniffer/cli-kit + pin argc

[Deniffer001]

Migrates all 7 product CLIs onto the extracted @deniffer/cli-kit base, and pins argc to stop github-main drift.

CLIs migrated

backlink · gsc · google-ads · page-extract · posthog · serp-snapshot · sitemap-watch

Each now builds its admin-CLI runtime on cli-kit instead of a local copy:

• lib/errors.ts → cli-kit/errors; the per-provider HTTP-status/code classification is kept as a *ErrorMapper plugged into the cli-kit normalizer seam (behavior preserved exactly).
• output.ts → cli-kit/output (gsc / google-ads / sitemap keep their legacy pretty-mode line format via the human override; JSON output + normalization run on cli-kit).
• services.ts → cli-kit/services lazy container + defineClientAdapter (each provider injected as the adapter); the getXClient() accessor is preserved so handlers/command-support stay untouched.
• adds vitest.config.ts inlining @deniffer/cli-kit (it ships bun-native .ts that vite does not transpile in node_modules by default).

Untouched in every package: provider/client, context, index.ts, handlers/, lib/command-support.ts, schema.ts, lib/input-validation.ts, all test files.

argc pinned

github:ethan-huo/argc was unpinned everywhere, so any install silently drifted main (it bit this work mid-PR). Pinned to #b18dad5 (current latest, verified green) across all 7 packages + the workspace catalog.

Verification

• check-types → all 7 exit 0
• test:once → 113 tests pass (5+4+4+13+32+28+27), counts unchanged from baseline
• cli-kit consumed at #v0.1.2

Dogfooding this surfaced one upstream fix in cli-kit (error envelopes → stderr, shipped as v0.1.1).