Spec: selfhoster config surface + docs for the planning routine

[JSONbored]

Problem

There is no .loopover.yml surface for configuring this new planning tool's behavior (default draft/create posture override, label-taxonomy preferences, milestone-reuse preferences), and no docs page explains the capability to selfhosters.

Area

.loopover.yml schema/parser, apps/loopover-ui (self-host docs pages).

Proposal

• Add a scoped .loopover.yml section (e.g. a new issuePlanning: key) covering: opt-in/out, default draft/create posture override, and label/milestone preferences.
• Add a docs page under apps/loopover-ui explaining what the MCP tool does, its draft-by-default safety model, and how to invoke it — matching the structure of existing self-host docs pages (e.g. docs.self-hosting-unified-ams-orb.tsx).

Deliverables

• .loopover.yml schema addition + validation for the new issuePlanning section.
• Docs page covering usage, safety defaults, and gittensor-optional behavior.

Resources

• Existing .loopover.yml schema/parser location and validation pattern.
• apps/loopover-ui's existing self-host docs pages for structure precedent.

Boundaries

• Docs/config only — no new runtime behavior beyond what sub-issues 1-4 already define.
• Depends on sub-issues 1-4 being scoped (doesn't block on full implementation, but should reflect the decided shape of each).

[linear-code]

JSO-5290