docs: scaffold documentation information architecture (Phase 1)

Add the docs/ skeleton for the full docs implementation: getting-started,
architecture, guides, reference, and vision sections, with a nav/TOC home
page. Every page is a stub carrying its heading outline and pointers to the
source material to be migrated in Phase 2 (content).

docs/nips/, docs/spec/, and the loose design docs stay at their current
paths (55 references from code, tests, and migrations outside docs/);
reference/nips.md and reference/design-docs.md index them instead.

Root GitHub-convention files are untouched. ARCHITECTURE/NOSTR/TESTING/
RELEASING/VISION* remain in place this phase and will become pointer files
in Phase 2.

Co-authored-by: npub19zza5yyr075j4vvlg2drsh2xe0xy3dqxhfchlgtw8vryglrry3gq8q7tzk <2885da10837fa92ab19f429a385d46cbcc48b406ba717fa16e3b06447c632450@sprout-oss.stage.blox.sqprod.co>
Signed-off-by: npub19zza5yyr075j4vvlg2drsh2xe0xy3dqxhfchlgtw8vryglrry3gq8q7tzk <2885da10837fa92ab19f429a385d46cbcc48b406ba717fa16e3b06447c632450@sprout-oss.stage.blox.sqprod.co>

docs/getting-started/installation.md

@@ -0,0 +1,20 @@
+# Installation
+
+> **Status: stub — Phase 1 (structure).** Content to be written in Phase 2.
+>
+> **Scope:** How to install Buzz on each platform (desktop app, relay binary, CLI, mobile). New content.
+
+## Outline
+
+- Supported platforms
+- Desktop app (macOS/Windows/Linux)
+- Relay (binary, Docker)
+- CLI (`buzz`)
+- Mobile (iOS/Android status)
+- Verifying the install
+
+## Source material
+
+- `README.md` (intro, install pointers)
+- `RELEASING.md` §Platform Support, §What Gets Published
+- `Dockerfile`, `docker-compose.yml`

docs/getting-started/local-relay.md

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+# Running a Local Relay
+
+> **Status: stub — Phase 1 (structure).** Content to be written in Phase 2.
+>
+> **Scope:** Full local-relay workflow for development: build, run, smoke-test with the CLI.
+
+## Outline
+
+- Build and run options (cargo, just recipes)
+- Debug vs release gotchas
+- Smoke-testing with `buzz` CLI (keypair, channel, messages, threads)
+- Troubleshooting
+
+## Source material
+
+- `TESTING.md` §Live Local Relay, §Troubleshooting
+- `Justfile` relay recipes

docs/getting-started/quickstart.md

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+# Quickstart
+
+> **Status: stub — Phase 1 (structure).** Content to be written in Phase 2.
+>
+> **Scope:** Zero-to-first-message: start a relay, create a channel, send a message, mention an agent. New content synthesized from README + TESTING.
+
+## Outline
+
+- Prerequisites
+- Start a local relay
+- Create your identity and a channel
+- Send and read messages
+- Add an agent and @mention it
+- Where to go next
+
+## Source material
+
+- `README.md`
+- `TESTING.md` §Live Local Relay (steps 1–4), §ACP Harness
+- `examples/countdown-bot`, `examples/meadow-core` (pointer)