docs(maintainers): define the feature proposal workflow (#7000)

The handbook says substantial features need Product Owner approval
before implementation, but not how a proposal gets there, what counts
as substantial, or what happens when no answer comes. Add the full
workflow: triage within 7 days, a decision brief, four product labels,
a lazy-consensus timeout that only applies to big-but-reversible work,
and definitions for every judgement call (small, big, reversible, new
direction, fits ROADMAP, objection, recorded decision).

The Feature Request form gets three optional fields for the brief, and
the PR template, CONTRIBUTING and triage point at the workflow.

.github/ISSUE_TEMPLATE/feature_request.yml

@@ -14,6 +14,8 @@ body:
         If your idea needs community input before it becomes a concrete proposal,
         start a [discussion](https://github.com/odysseus-dev/odysseus/discussions/categories/ideas) instead.
 
+        How a proposal is triaged and decided: [product and feature proposals](https://github.com/odysseus-dev/odysseus/blob/dev/docs/maintainers/product-and-features.md#feature-proposal-workflow).
+
   - type: checkboxes
     id: prerequisites
     attributes:
@@ -79,6 +81,32 @@ body:
       label: Prior Art / Related Issues
       description: Link any related issues, discussions, or external references that informed this proposal.
 
+  - type: dropdown
+    id: scope
+    attributes:
+      label: Size and reversibility
+      description: Your best guess; the triager decides. Definitions are in the maintainer handbook (product-and-features.md).
+      multiple: true
+      options:
+        - "Small, reversible change within ROADMAP"
+        - "Big (more than one PR, or changes existing default behaviour)"
+        - "New direction (new area, multi-user, data leaving the machine, ...)"
+        - "Hard to undo (migration, deleted data, changed contract or permissions)"
+        - "Not sure"
+
+  - type: textarea
+    id: decision_questions
+    attributes:
+      label: Questions for the Product Owner
+      description: If this needs a product decision, the exact yes/no questions — one per independent part.
+      placeholder: "1. Should notes be shareable between accounts on one instance? (yes/no)"
+
+  - type: textarea
+    id: evidence
+    attributes:
+      label: Screenshots, recording or demo
+      description: For anything that renders, attach screenshots or a short recording. Link a demo branch if you have one.
+
   - type: dropdown
     id: willing_to_implement
     attributes: