bip85: address review on Nostr application, renumber to 128002'

Incorporate akarve's review of the Nostr application:

- Renumber 9000' -> 128002' and drop the origin explanation,
  per the convention of leaving the app number's meaning implicit.
- State explicitly that the Nostr private key is the first 32 bytes
  (most significant 256 bits) of the 64-byte BIP-85 entropy.
- Move the private-key sentence below the path and consolidate it
  with the encoding description.
- Justify the reserved identity 0' and account 0' indices.
- Show the full 64-byte DERIVED ENTROPY in all test vectors for
  consistency with the other applications.

Author: ethicnology

bip-0085.mediawiki

@@ -425,49 +425,45 @@ OUTPUT
 
 ===Nostr===
 
-Application number: 9000'
+Application number: 128002'
 
-9000 is the zip code of Funchal in Madeira, Portugal, where this specification was written during the Sovereign Engineering event.
+The derivation path format is: <code>m/83696968'/128002'/{identity}'/{account_index}'</code>
 
-The derivation path format is: <code>m/83696968'/9000'/{identity}'/{account_index}'</code>
+Each <code>identity</code> is an independent, unlinkable Nostr key namespace, and each <code>account_index</code> is a distinct key within that identity.
 
-Uses the entropy as a Nostr private key.
+Identity index <code>0'</code> is reserved for future protocol-level use. Within every identity, account index <code>0'</code> is reserved as a management key for that identity (for example proof-of-linkage between an identity's keys, key rotation, and revocation). Usable signing keys therefore start at <code>identity >= 1'</code> and <code>account_index >= 1'</code>. The exact semantics of these reserved indices are defined by an external NIP that references this application.
 
-Identity index <code>0'</code> is reserved for future protocol use.
-Account index <code>0'</code> is reserved across all identities for key management operations.
-Usable keys start at <code>identity >= 1'</code> and <code>account_index >= 1'</code>.
-
-The resulting 32-byte private key is Bech32 encoded as an <code>nsec</code> per NIP19.
+The standard application of BIP-85 produces 64 bytes of entropy. Take the first 32 bytes (the 256 most significant bits) as the Nostr private key and discard the trailing 32 bytes, as in the HEX application. This 32-byte private key is then Bech32 encoded as an <code>nsec</code> per NIP19.
 
 '''identity=1, account=1'''
 
 INPUT:
 * MASTER BIP32 ROOT KEY: xprv9s21ZrQH143K2LBWUUQRFXhucrQqBpKdRRxNVq2zBqsx8HVqFk2uYo8kmbaLLHRdqtQpUm98uKfu3vca1LqdGhUtyoFnCNkfmXRyPXLjbKb
-* PATH: m/83696968'/9000'/1'/1'
+* PATH: m/83696968'/128002'/1'/1'
 
 OUTPUT
-* DERIVED ENTROPY=552ad1d578fe1bc927cec9612651652b07c52dde4017911bc23bc953568075ff
-* DERIVED NSEC=nsec1254dr4tclcdujf7we9sjv5t99vru2tw7gqtezx7z80y4x45qwhlsmxapst
+* DERIVED ENTROPY=ff6eb0fcdf1ef87a2a06b0d7884d495b486d0faa210e9f80f23fd649d6e114d27873d12f3b57c469f684e4dc9f4abf10beeacb59b385fde8e33f1947bc5c6c17
+* DERIVED NSEC=nsec1lahtplxlrmu852sxkrtcsn2ftdyx6ra2yy8flq8j8ltyn4hpznfq23uvqz
 
 '''identity=1, account=2'''
 
 INPUT:
 * MASTER BIP32 ROOT KEY: xprv9s21ZrQH143K2LBWUUQRFXhucrQqBpKdRRxNVq2zBqsx8HVqFk2uYo8kmbaLLHRdqtQpUm98uKfu3vca1LqdGhUtyoFnCNkfmXRyPXLjbKb
-* PATH: m/83696968'/9000'/1'/2'
+* PATH: m/83696968'/128002'/1'/2'
 
 OUTPUT
-* DERIVED ENTROPY=4fd36c0061a65db375b4350f44bb62a6d7f716ee93bd0f59887ac50b35fa8b96
-* DERIVED NSEC=nsec1flfkcqrp5ewmxad5x585fwmz5mtlw9hwjw7s7kvg0tzskd063wtq34wlgr
+* DERIVED ENTROPY=917628689652288f6983c8a01db516d0697d5198dcf9de9010597f5e322fba6e435a731d85fbcc5768c06ff95ff34bf577f63f415cb170473659753acf14722d
+* DERIVED NSEC=nsec1j9mzs6yk2g5g76vrezspmdgk6p5h65vcmnuaayqst9l4uv30hfhqje0jyh
 
 '''identity=2, account=1'''
 
 INPUT:
 * MASTER BIP32 ROOT KEY: xprv9s21ZrQH143K2LBWUUQRFXhucrQqBpKdRRxNVq2zBqsx8HVqFk2uYo8kmbaLLHRdqtQpUm98uKfu3vca1LqdGhUtyoFnCNkfmXRyPXLjbKb
-* PATH: m/83696968'/9000'/2'/1'
+* PATH: m/83696968'/128002'/2'/1'
 
 OUTPUT
-* DERIVED ENTROPY=b2d3b48992d46f98beac0196c4e258417087e467dbec1503342785368f4402c2
-* DERIVED NSEC=nsec1ktfmfzvj63he304vqxtvfcjcg9cg0er8m0kp2qe5y7zndr6yqtpq7q5y44
+* DERIVED ENTROPY=fa2e784291b1fd347ba3624672e3090cb2cee34b8567180336e3aa290d02715b8f4b18f02f07cb2aa3023afd34735282cc6594370f47e6e1fa48d8d0dda93096
+* DERIVED NSEC=nsec1lgh8ss53k87ng7arvfr89ccfpjevac6ts4n3sqekuw4zjrgzw9dsq3uelh
 
 ==Backwards Compatibility==
 
@@ -489,7 +485,7 @@ BIP32, BIP39, [https://github.com/nostr-protocol/nips/blob/master/01.md NIP01],
 
 ====Added====
 
-* Nostr application 9000'
+* Nostr application 128002'
 
 ===2.0.0 (2025-09-19)===