docs: delete scope-doc text with no live producer

[MattDHill]

Phase 2 of the docs cruft audit: all 65 AGENTS.md / ARCHITECTURE.md / CONTRIBUTING.md files, at every scope, read end to end.

Same rule as the guide pass — a sentence citing what not to do, what not to include, or a mistake once made only earns its place if you can name the live producer. No producer, delete. 53 deletions across 29 files; 200 prohibitions and incident narrations examined and kept, each with a named producer.

Things that were simply wrong

These are the ones worth reading the diff for.

Doc	Claim	Reality
projects/start-registry/CONTRIBUTING.md	Cargo version "tracks the OS release line — don't bump it independently"	start-registry is 1.0.2, StartOS is 0.4.0.2. The crate's own AGENTS.md, one directory over, says the opposite. This is the retired rule stated as current.
projects/start-registry/AGENTS.md	"(currently 1.0.0)"	Already 1.0.2.
shared-libs/crates/rpc-toolkit/CONTRIBUTING.md	"This crate ships a rustfmt.toml"	It does not; only the repo root has one.
projects/start-sdk/AGENTS.md	build table documents make dist	Not a target in that Makefile. (start-core's make dist, referenced further down the same file, is real and stays.)
ARCHITECTURE.md	apt/ under projects/start-os/	apt/ is at the repo root.
shared-libs/CONTRIBUTING.md	ts-modules' "current contents are Angular libraries"	It also holds the non-Angular start-core.
projects/start-registry/ARCHITECTURE.md	"All five product binaries"	Root AGENTS.md counts six.
projects/start-sdk/ARCHITECTURE.md	—	AGENTS.md listed twice in Further reading.

Migration narration whose migration is over

Four separate stale-path notes mapped the pre-monorepo root layout (core/, web/, sdk/, patch-db/, container-runtime/). The root AGENTS.md keeps one — core/src/ is still referenced live in projects/start-os/DEV_TODO.md, so the mapping is still reachable, and one line is the maximum the still-encounterable rule allows. The copies in start-cli, container-runtime and shared-libs go, along with "Internally unchanged from the old core/ crate", the start-fs migration note, the retired submodule's workspace Cargo.toml, and the base/lib/... import shape.

Same treatment for the in-flight CONTRIBUTING.md → AGENTS.md migration: the rule for how to migrate stays in all three places it appears; the three tallies of which scopes have migrated go. A reader can determine that by looking, and the next scope to migrate silently falsifies a written count.

Counts and in-progress markers

~430 tests (twice), 11 modules (twice), ~28 utility modules, ~117-line, ~2200 lines, 3 small build-infra patches, the SDK/OS version pair, (currently by start-core), (currently just bitcoin-guides), (currently the Angular libs shared and marketplace) (twice), being replaced, being phased out, two notes recording which warnings a crate happened to emit, and a commented-out list of ten aspirational locales.

Plus "the standalone Start9Labs/patch-db repo is being retired" — worse than stale: gh api shows the repo unarchived and pushed to after that line was written, so a reader who checks cannot tell whether the doc is wrong or the retirement stalled.

Kept against the extraction pass's recommendation

Each of these was flagged for deletion and I disagreed; producer named.

• projects/start-wrt/web/CONTRIBUTING.md — the taiga-ui-mcp entry. Flagged as a beta tool. It is one of the three sanctioned ways to verify a Taiga API in the frontend workflow; deleting it would contradict live guidance.
• projects/brochure-marketplace/AGENTS.md — "Don't add a parallel state store." The pass found no copyable neighbour, which is true, but the producer here is the obvious-but-wrong fix: an agent adding a feature that needs registry state stands up its own service instead of extending MarketplaceService. The preceding sentences say where state lives; they do not forbid adding a second one.
• shared-libs/crates/jsonpath/AGENTS.md — "Do not add new FFI here." src/ffi/mod.rs is a working exported C ABI and lua/jsonpath.lua dlopens it in-tree. That is a neighbouring example, literally.
• projects/start-registry/AGENTS.md — "no longer tied to the StartOS release line." The shared # VERSION_BUMP marker sits on this crate exactly as on the OS-coupled ones, and VERSION_BUMP.md is titled the StartOS version bump guide, so the wrong inference is one glance away.
• Root AGENTS.md — the stale-path watch, and root CONTRIBUTING.md — the next/* mapping line. Both are the single surviving pointer for a dead thing still reachable in a live artifact. Two agents independently proposed deleting each half of a pair; taking both would have removed the pointer entirely.

Wants a decision — not resolved here

1. projects/start-wrt/CONTRIBUTING.md:61 — "The OpenWrt image build needs a consistent environment — Docker is recommended; native builds on some distros fail silently." The Docker half is dead: build.mk runs make -C on the host with no container, and CI builds the image natively on ubuntu-latest. But the second half warns about the only path the repo offers, and I cannot tell from the tree whether that environment sensitivity is real. If it is, the sentence needs rewriting rather than deleting; if it is not, the whole thing goes.
2. projects/start-wrt/AGENTS.md:13 and :16 — the "start-wrt was migrated from its own repo" lead-in and "the old embedded start-os submodule is gone". Both are completed-migration history, but the first introduces a heading and a five-bullet list of durable facts, and the second is mid-sentence in a clause explaining a genuinely non-obvious live fact (a dependency named startos that is really the start-core package). Cleaning these is a structural re-cut, not a deletion, so I left them.

Separate finding, not a docs issue

13 remote branches still carry - next/* workflow trigger lines, several with open PRs (#3617, #3622, #3623, #3607, #3573, #3137). The triggers were removed from master in 7695ab1ff; those branches predate it and will restore them on merge. Worth a sweep independently of this PR — it is also why the mapping line in the root CONTRIBUTING.md is kept.