feat(repo): flow-pack E1 — foundation (/flow-prime + rule + tracked contract + labels/milestone)

[w7-mgfcode]

Sub-issue of #368 (umbrella: integrate flow-pack methodology as the flow: command suite)

Foundation Epic — blocks Epics E2–E5.

Purpose

Land the durable contract + the first command + project setup so the rest of the suite can be built on a stable base.

Sub-tasks

• Write tracked contract docs/flow-pack-methodology.md (Mermaid + invariants + FLAI mapping + portability manifest + fresh-clone recovery section).
• Write tracked command template docs/flow-pack/commands/flow-prime.md.
• Install local runtime copy .claude/commands/flow/flow-prime.md (regenerable from the tracked template; not the durable source).
• Write local rule .claude/rules/umbrella-issue.md (durable narrative lives in the methodology doc).
• /flow-prime runs: prime (codebase, delegating core_piv_loop:prime) + locate (gh state) + writes .flow/state.md.
• Labels umbrella/epic/flow + milestone exist.

Acceptance criteria

• Tracked docs committed: docs/flow-pack-methodology.md + docs/flow-pack/commands/flow-prime.md.
• Local .claude/commands/flow/flow-prime.md present, regenerated from the tracked template (explicitly not the durable committed source).
• Documented fresh-clone recovery reproduces the local command from tracked docs.
• /flow-prime produces a current-workflow-map + a you-are-here snapshot.

Phase: Foundation. Hand-off on completion: base_prp:prp-create.
Provenance: reverse-engineered from ai_engineering_mermaid_flow_pack/docs/flow-analysis/01-decomposition.md.

[w7-mgfcode]

Closed by PR #370 (merged a921ecb). E1 foundation delivered: /flow-prime command, umbrella-issue.md rule, docs/flow-pack/commands/flow-prime.md tracked contract, labels/milestone setup.