feat(canon): add inter-repo communication standard with todo taxonomy

Establishes the repo boundary rule and a formal vocabulary for classifying
work items by scope:

- Task: neutral state hub data entity
- Todo: a task scoped to the current session's repo/domain
  - Internal todo: addressed within this repo by this agent
  - Ecosystem todo: work for another registered repo → state hub task [repo:<slug>]
  - Third-party todo: work for an upstream repo → contribution artifact (BR/FR/EP/UPR)

New dashboard doc: /docs/inter-repo-communication — defines the boundary rule,
the full terminology, ecosystem and third-party todo workflows, and a decision
table for classifying any piece of work found during a session.

Also:
- sbom.md: replace verbose inter-repo section with a 3-line summary + link
- observablehq.config.js: add "Inter-Repo Communication" to Reference nav
- project_claude_md.template: add "### Repo Boundary Rule" section; fix
  Workplan Convention section (removing incorrect claim that the custodian
  writes workplan files in other repos — that is the target repo's job)

Cross-repo: created state hub task [repo:railiance-bootstrap] for that repo's
agent to apply the boundary rule and workplan convention fix to its own CLAUDE.md
(task 78d43cb0, workstream 59155efb).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/project_claude_md.template

@@ -59,6 +59,22 @@ If there are no workstreams at all: follow the First Session Protocol below.
 
 ---
 
+### Repo Boundary Rule
+
+This agent is responsible for files **in this repo only**.
+
+- **Do not** write files or make commits in any other repository
+- **Do not** create workplan files in other repos on their behalf
+- When you identify work for another registered repo (**ecosystem todo**):
+  create a state hub task with `[repo:<slug>]` in the title — the other repo's
+  agent will see it at session start and create its own workplan
+- When you identify work for an upstream repo (**third-party todo**):
+  create a contribution artifact in `contrib/` and register it
+
+Terminology and workflows: `http://localhost:3000/docs/inter-repo-communication`
+
+---
+
 ### First Session Protocol
 
 Triggered when `get_state_summary()` shows **no workstreams** for the `{DOMAIN}`
@@ -108,10 +124,10 @@ Work items MUST originate as files in this repo before being registered in the h
 **Frontmatter required:** `id`, `type: workplan`, `domain`, `repo`, `status`,
 `state_hub_workstream_id`, `state_hub_task_id` (per task)
 
-When the custodian creates a task targeting this repo from another session, it:
-1. Creates a state hub task with `[repo:{REPO_SLUG}]` in the title
-2. Creates a workplan file in this repo's `workplans/`
-3. You will see both at session start via the orientation sequence above
+When another domain's agent identifies work for this repo, it creates a state hub
+task with `[repo:{REPO_SLUG}]` in the title (an **ecosystem todo**). You will
+see it at session start via `get_state_summary()`. When you pick it up, create
+the corresponding workplan file in `workplans/` (ADR-001) and begin work.
 
 ---