Improve Docker mesh setup: data-driven topologies, identity derivation, services

Config system overhaul:
- Add mesh-public topology (5 Docker nodes + external pub node at 217.77.8.91)
- Refactor generate-configs.sh to read topology YAML files directly,
  replacing hardcoded lookup functions, with multi-char node ID support
- Generate npubs.env with all node npubs; sourced by test scripts and
  injected into containers via docker-compose env_file directive
- Add .env with COMPOSE_PROFILES=mesh so docker compose defaults to
  mesh topology without requiring --profile

Deterministic mesh identity derivation:
- Add derive-keys.py: pure Python tool (no deps) deriving nsec/npub
  from sha256(mesh-name|node-id) via secp256k1 and BIP-173 bech32
- generate-configs.sh and build.sh accept optional mesh-name argument;
  Docker node identities are derived while external nodes keep
  hardcoded keys from topology YAML

Docker compose improvements:
- Add mesh-public profile service definitions
- build.sh now runs docker compose build automatically, providing a
  single command for the full binary+configs+images pipeline
- Ping test script supports mesh-public topology

Container services:
- Add HTTP server on port 8000 (IPv6-bound) serving static page,
  accessible over FIPS overlay via npub.fips hostnames
- Add rsync to container packages

Documentation:
- Comprehensive README update covering topology system, identity
  derivation, npubs.env, and container background services (SSH,
  iperf3, HTTP) with usage examples

examples/docker-network/scripts/derive-keys.py

@@ -0,0 +1,111 @@
+#!/usr/bin/env python3
+"""Derive deterministic nostr nsec/npub from mesh-name and node-name.
+
+Usage: derive-keys.py <mesh-name> <node-name>
+Output: nsec=<hex>\nnpub=<bech32>
+
+Derivation: nsec = sha256(mesh_name + "|" + node_name)
+            npub = bech32("npub", secp256k1_pubkey_x(nsec))
+
+Pure Python, no external dependencies.
+"""
+
+import hashlib
+import sys
+
+# --- secp256k1 ---
+
+P = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F
+Gx = 0x79BE667EF9DCBBAC55A06295CE870B07029BFCDB2DCE28D959F2815B16F81798
+Gy = 0x483ADA7726A3C4655DA4FBFC0E1108A8FD17B448A68554199C47D08FFB10D4B8
+
+
+def _modinv(a, m):
+    return pow(a, m - 2, m)
+
+
+def _point_add(p1, p2):
+    if p1 is None:
+        return p2
+    if p2 is None:
+        return p1
+    x1, y1 = p1
+    x2, y2 = p2
+    if x1 == x2 and y1 != y2:
+        return None
+    if x1 == x2:
+        lam = (3 * x1 * x1) * _modinv(2 * y1, P) % P
+    else:
+        lam = (y2 - y1) * _modinv(x2 - x1, P) % P
+    x3 = (lam * lam - x1 - x2) % P
+    y3 = (lam * (x1 - x3) - y1) % P
+    return (x3, y3)
+
+
+def _scalar_mult(k, point):
+    result = None
+    addend = point
+    while k:
+        if k & 1:
+            result = _point_add(result, addend)
+        addend = _point_add(addend, addend)
+        k >>= 1
+    return result
+
+
+# --- bech32 (BIP-173) ---
+
+_CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
+
+
+def _bech32_polymod(values):
+    gen = [0x3B6A57B2, 0x26508E6D, 0x1EA119FA, 0x3D4233DD, 0x2A1462B3]
+    chk = 1
+    for v in values:
+        b = chk >> 25
+        chk = (chk & 0x1FFFFFF) << 5 ^ v
+        for i in range(5):
+            chk ^= gen[i] if ((b >> i) & 1) else 0
+    return chk
+
+
+def _bech32_encode(hrp, data_5bit):
+    hrp_expand = [ord(x) >> 5 for x in hrp] + [0] + [ord(x) & 31 for x in hrp]
+    polymod = _bech32_polymod(hrp_expand + data_5bit + [0] * 6) ^ 1
+    checksum = [(polymod >> 5 * (5 - i)) & 31 for i in range(6)]
+    return hrp + "1" + "".join(_CHARSET[d] for d in data_5bit + checksum)
+
+
+def _convertbits(data, frombits, tobits):
+    acc, bits, ret = 0, 0, []
+    maxv = (1 << tobits) - 1
+    for value in data:
+        acc = (acc << frombits) | value
+        bits += frombits
+        while bits >= tobits:
+            bits -= tobits
+            ret.append((acc >> bits) & maxv)
+    if bits:
+        ret.append((acc << (tobits - bits)) & maxv)
+    return ret
+
+
+# --- public API ---
+
+def derive(mesh_name, node_name):
+    nsec_hex = hashlib.sha256(f"{mesh_name}|{node_name}".encode()).hexdigest()
+    k = int(nsec_hex, 16)
+    pub = _scalar_mult(k, (Gx, Gy))
+    x_hex = format(pub[0], "064x")
+    data_5bit = _convertbits(list(bytes.fromhex(x_hex)), 8, 5)
+    npub = _bech32_encode("npub", data_5bit)
+    return nsec_hex, npub
+
+
+if __name__ == "__main__":
+    if len(sys.argv) != 3:
+        print(f"Usage: {sys.argv[0]} <mesh-name> <node-name>", file=sys.stderr)
+        sys.exit(1)
+    nsec, npub = derive(sys.argv[1], sys.argv[2])
+    print(f"nsec={nsec}")
+    print(f"npub={npub}")