feat: sync CLI registry with memory type + categories

[nsollazzo]

Summary

• Add memory to api.ListingTypes (platform order after mcp) → positronick memory search|list|show|install
• Add shared api.ListingCategories including Memory and Observability; mockadmin validates against it
• Update skill contract, README, MCP tools/docs, admin help, CHANGELOG

Why

Platform #163 added the memory listing type and Memory/Observability categories. Released CLI v0.1.2 and previous main still omitted them, so install.sh users and even our alpha binary could not talk to the full registry model (unknown command "memory").

Test plan

• go test ./... -race — all packages PASS
• TestSkillPinsTargetAndTypeLists — PASS
• TestListingTypesMatchPlatformOrder / TestListingCategoriesMatchPlatformOrder
• Smoke: built binary memory list --json --base-url https://positronick.com → {"count":0,"listings":[]} (not unknown command)
• Existing mcp list still works against prod

Follow-ups (not this PR)

• Tag v0.1.3 after merge so install.sh leaves v0.1.2
• Engine ListingTypes still missing memory — separate PR on Positronick/engine
• Optional later: pass ?q= / ?category= through to server listings API

Notes

• No promote/billing CLI surface (YAGNI)
• Does not change existing JSON shapes except additive memory noun + goldens

[nsollazzo]

Agent review · Positronick CLI

Reviewer: Daneel (Gate B)
PR: #43 · Head: ef41f41
Skills: grok (implement) · requesting-code-review (local race/smoke) · github product-pr Gate B
Verdict: APPROVE

Models & effort

Role	Model	Effort / mode
Orchestrator (Daneel)	grok-4.5	session
Implementer	Grok Build CLI	headless --always-approve
Gate A	local go test ./... -race + prod smoke	n/a
Gate B author	grok-4.5	session
Secondary	not used	—

Spec compliance

• memory in api.ListingTypes after mcp (platform order)
• api.ListingCategories includes Memory + Observability; mockadmin shared
• positronick memory noun + skill contract pin
• No promote CLI / no engine changes (YAGNI)

Tests run

• go test ./... -race — PASS
• Built binary: memory list --json against https://positronick.com → count:0 (valid empty; not unknown command)
• mcp list still works against prod

Blockers

None.

Should-fix

None for merge.

Nits / follow-ups (post-merge)

1. Tag v0.1.3 so install.sh leaves v0.1.2
2. Engine ListingTypes still missing memory
3. golangci-lint local env is go1.25 vs project 1.26.5 — pre-existing toolchain pin, not introduced here

Nick merges. No merge from agent.