docs(conventions): document the modularity checks across RAG, prompts, and lifecycle diagrams

Make the docs and role prompts match the shipped modularity enforcement. The standards doc gains a Modularity section (cohesion / thin routes / thin components / god class, scan-derived + language-aware); the developer prompt tells agents to write modular code (thin routes that delegate, one concern per file, components that delegate to hooks) and that block-level findings refuse i_am_done; QA + PR-reviewer prompts note the modularity findings in evidence / the pr_pass block. Also fixes the two lifecycle diagrams (usage.md, roboco/models/README.md) that omitted the awaiting_pr_review gate.

usage.md

@@ -129,8 +129,14 @@ Enum values: `task_type` ∈ {`code`, `documentation`, `research`, `planning`, `
 pending → claimed → in_progress → verifying → awaiting_qa → awaiting_documentation → awaiting_pm_review → completed
                          ↓                                                                    ↓
                     blocked/paused                                                  awaiting_ceo_approval (major tasks)
+
+in_progress → awaiting_pr_review → awaiting_pm_review → completed   (in-path PR-review gate for assembled PRs)
+                     ↓
+              needs_revision (pr_fail)
 ```
 
+The leaf flow above is the developer path. Assembled PRs add an in-path PR-review gate: the cell PM's `submit_up` opens the cell→root PR and the Main PM's `submit_root` opens the root→master PR, each moving the task `in_progress → awaiting_pr_review`. There the PR reviewer `pr_pass`es it on to `awaiting_pm_review` or `pr_fail`s it back to `needs_revision`. Leaf developer tasks and branchless coordination roots skip the gate.
+
 Agents automatically:
 1. Pull pending work via the gateway verb `give_me_work()`
 2. Claim it with `i_will_work_on(task_id)` (auto-creates the feature branch)