docs: reconcile Phase 2 plugin lifecycle

[xiayh17]

Outcome

Reconciles the checked-in Phase 2 plugin documents with the implementation and acceptance evidence already merged by #102.

Changes

• renames the accepted Phase 2 design and P2-1 through P2-4 contracts from active- to implemented-;
• updates the central cross-review matrix and the Phase 2.5 dependency link;
• records Complete Phase 2 workspace plugin runtime #102 as the actual upstream merge instead of the historical branch-local PR 使用Deepseek模型报错“timed out waiting for desktop Agent R authentication” #2 reference;
• updates every deterministic contract check that reads the renamed files.

No runtime, schema, permission, UI, version, NEWS, release or distribution behavior changes.

Verification

• node --check passed for all 16 affected contract scripts;
• all 16 affected scripts passed with --test;
• no references to the five obsolete active- paths remain;
• git diff --check passed.

Governance

Change class: D3 lifecycle fact, documentation-only R0 reconciliation. The owning contracts already record full implementation, hosted validation and installed acceptance. Release, public distribution, Phase 2.5 and Phase 3 remain separately gated.

Related tracker: #17
Next usable-author-path package: #104