docs: correct ARCHITECTURE.md and BUILDING.md against the current tree

[adamXbot]

Both files predate most of the codebase and had drifted far enough to actively mislead.

The one that cost me an hour

ARCHITECTURE.md states that PfctlKillSwitch.swift "isn't committed yet", and the audit-flow diagram labels the network kill switch "planned". It ships and works.

The cause is worth fixing properly: there are two helper source trees.

Path	Contents	Built?
privacycommand/privacycommandHelper/	5 sources incl. PfctlKillSwitch.swift	Yes — this is what the Xcode project references
privacycommand/Sources/privacycommandHelper/	4 sources, 29 lines shorter, no kill switch	No — vestigial

ARCHITECTURE.md was describing the stale one. I've corrected the path, the file list, and the diagram, and explicitly flagged that the Sources/ copy exists and should be deleted — anyone who edits the wrong tree will spend a while wondering why nothing changes. I haven't deleted it in this PR, since that's a code change rather than a docs fix; happy to follow up.

ARCHITECTURE.md — counts

	Was	Is
Detectors	29	41
Monitoring files	11	12
SwiftUI files	59	63
Total Swift	~100	229
Commits	"six commits old"	89

Also: "The four targets" heads a table listing seven, and the intro sentence was truncated mid-clause — now completed and pointed at the sibling design docs.

BUILDING.md

This one was worse — following it verbatim does not produce a build.

• Wrong path. cd "MacOS Permissions/privacycommand" — that folder no longer exists.
• Wrong bundle ID. com.example.privacycommand, in two places. It's org.privacykey.privacycommand, with .HelperTool and .tests.
• Wrong targets. Claimed two targets and "all 31 Swift sources" in a single app target. There are five Xcode targets; the app alone has 63 sources.
• Sparkle was missing entirely. A fresh checkout doesn't build without adding the package dependency. The README documents this; BUILDING.md didn't.
• Added the helper Team ID requirement as failure mode 0. It's the most likely thing to go wrong, it builds cleanly and only fails at runtime, and it takes out file monitoring, the BTM audit and the kill switch simultaneously.
• Retitled "What I would expect to fail first on a real build" — written before the project had ever been built — to describe what actually trips people.

Scope

Docs only; no code touched. User-facing documentation now lives at privacykey/docs-privacycommand, so these two files are explicitly the internal pair.