docs: fix stale kind count, quick-start numbering, and empty Further Reading (#2613)

## Problem

Three small documentation defects, each verified against the code at
06e3d82b:

1. **ARCHITECTURE.md (Event Kinds section)** says `buzz-core` defines
"all 81 kinds". The registry has grown: `ALL_KINDS` in
`crates/buzz-core/src/kind.rs` now has **127** entries (all unique
values). The sentence also says every kind is `pub const KIND_*`, but
registry entries such as `RELAY_ADMIN_ADD_MEMBER` do not use that
prefix.

2. **NOSTR.md Quick Start** numbers its steps 1, 2, 3, 5 — there is no
step 4. PR #797 (2a038515) collapsed the old steps 1-4 (dropping the
separate "Start infrastructure" step) into 1-3, but the final "Connect
any NIP-29 + NIP-42 client" comment kept its old number 5.

3. **NOSTR.md "Further Reading"** is an empty heading — the section's
only content (a link to `crates/buzz-proxy/README.md`) was removed in PR
#1321 (14fba21e) along with the proxy crate itself, leaving a dangling
header as the last line of the file.

## Fix

1. Reworded the ARCHITECTURE.md sentence to defer to
`crates/buzz-core/src/kind.rs` as the source of truth, with the current
count (127) as an explicit "at the time of writing" snapshot, so the
sentence stays truthful as kinds are added. Also removed the incorrect
`KIND_*`-naming claim.
2. Renumbered the final quick-start step 5 → 4.
3. Populated Further Reading with three durable links: the upstream
nostr-protocol/nips repo, this repo's `docs/nips/` extension documents,
and `ARCHITECTURE.md`.

Docs-only; no code changes, no build impact.

## Verification (each claim ~30 seconds)

- Kind count: `python3 -c "import re;
s=open('crates/buzz-core/src/kind.rs').read(); m=re.search(r'ALL_KINDS:
&\[u32\] = &\[(.*?)\];', s, re.S); print(len([e for e in
m.group(1).split(',') if e.strip()]))"` → 127. All 127 values are
distinct. Non-`KIND_*` entry example: `RELAY_ADMIN_ADD_MEMBER` (kind.rs,
in `ALL_KINDS`).
- Missing step: `grep -n '^# [0-9]' NOSTR.md` on main shows `# 1.`, `#
2.`, `# 3.`, `# 5.` in the Quick Start block; `git show 2a038515 --
NOSTR.md` shows the renumbering that orphaned step 5.
- Empty section: `tail -1 NOSTR.md` on main is `## Further Reading` with
nothing after it; `git log -S'buzz-proxy/README' --oneline -- NOSTR.md`
shows the content removal in 14fba21e (#1321).

## Links

- `crates/buzz-core/src/kind.rs` — `ALL_KINDS` registry (source of truth
for the count)
- PR #797 / 2a038515 — introduced the step-numbering gap
- PR #1321 / 14fba21e — emptied the Further Reading section

Signed-off-by: Sean Gearin <sgearin@gmail.com>
Co-authored-by: Sean Gearin <sgearin@gmail.com>

ARCHITECTURE.md

@@ -139,7 +139,7 @@ The `kind` integer is the only dispatch switch. The relay routes, stores, and fa
 | 46001–46012 | KIND_WORKFLOW_* | Workflow execution events |
 | 20001 | KIND_PRESENCE_UPDATE | Ephemeral presence heartbeat |
 
-`buzz-core` defines all 81 kinds as `pub const KIND_*: u32` and exports `ALL_KINDS: &[u32]`. Kinds are `u32` (NIP-01 specifies unsigned integer; `u32` covers the full range). Buzz uses both standard Nostr kinds (e.g., kind 7 for reactions) and custom ranges (40000+).
+`buzz-core` defines each event kind as a `pub const u32` and exports the full registry as `ALL_KINDS: &[u32]` (127 kinds at the time of writing); `crates/buzz-core/src/kind.rs` is the source of truth for the current list. Kinds are `u32` (NIP-01 specifies unsigned integer; `u32` covers the full range). Buzz uses both standard Nostr kinds (e.g., kind 7 for reactions) and custom ranges (40000+).
 
 Note: `KIND_AUTH` (22242) is `pub const KIND_AUTH: u32` in `buzz-core/src/kind.rs` and imported by `buzz-relay/src/handlers/event.rs`. `KIND_CANVAS` (40100) is likewise `pub const KIND_CANVAS: u32` in `buzz-core/src/kind.rs`.