Cashu ecash chips: detect, render, and redeem tokens + /pay command (#1376)

* Cashu ecash chips: detect, render, and redeem tokens + /pay command

Content-level Cashu support, no wire-protocol changes:

- CashuTokenDecoder: summarizes V3 (cashuA base64url-JSON) tokens —
  amount summed across proofs, unit, mint host, memo — and V4 (cashuB)
  via a minimal bounded CBOR reader. All input is treated as
  adversarial: size caps, depth/item budgets, overflow guards, display
  sanitization; malformed payloads fail closed to a generic chip.
- PaymentChipView: cashu chips now show "500 sat · mint.example.com"
  (+ memo) instead of a generic label; tap opens a cashu: wallet URL
  and falls back to https://redeem.cashu.me when no wallet handles it;
  context menu adds copy token / redeem in wallet / redeem on web.
- extractCashuLinks now returns bare deduplicated bearer strings so the
  chip can decode them (cashu: URIs still detected via the embedded
  token).
- /pay <token>: validates the token decodes, sends it as the message
  body; DMs send directly, public channels require an explicit
  "/pay <token> public" confirm since tokens are bearer instruments.
  Suggested everywhere except public geohash channels.
- Tests: decoder (V3/V4 decode, summation, URI forms, truncation/
  garbage/huge fuzzing, CBOR depth bounds) and /pay command flows.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Cashu: strict decode on the /pay SEND path

The permissive decoder turned any non-empty cashuB… base64 that failed
CBOR parsing into a generic TokenInfo, so the /pay guard accepted base64
junk and truncated V4 tokens and relayed them with a success message.

Add a `strict` flag to CashuTokenDecoder.decode: in strict mode there is
no permissive V4 fallback and the token must resolve to a known version
with a positive amount, else it returns nil. Rendering keeps the
permissive path (an unknown chip is fine for display). /pay now decodes
with strict:true and surfaces "invalid cashu token" instead of sending.

Tests: /pay with truncated cashuB / base64 junk is rejected; valid V3
and valid definite-length V4 still send; decoder strict-mode unit tests.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: jack <jackjackbits@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

bitchat/Models/CommandInfo.swift

@@ -20,6 +20,7 @@ enum CommandInfo: String, Identifiable {
     case hug
     case message = "msg"
     case slap
+    case pay
     case unblock
     case who
     case favorite = "fav"
@@ -33,6 +34,8 @@ enum CommandInfo: String, Identifiable {
         switch self {
         case .block, .hug, .message, .slap, .unblock, .favorite, .unfavorite:
             return "<" + String(localized: "content.input.nickname_placeholder") + ">"
+        case .pay:
+            return "<" + String(localized: "content.input.token_placeholder") + ">"
         case .clear, .help, .who:
             return nil
         }
@@ -45,6 +48,7 @@ enum CommandInfo: String, Identifiable {
         case .help:         String(localized: "content.commands.help")
         case .hug:          String(localized: "content.commands.hug")
         case .message:      String(localized: "content.commands.message")
+        case .pay:          String(localized: "content.commands.pay")
         case .slap:         String(localized: "content.commands.slap")
         case .unblock:      String(localized: "content.commands.unblock")
         case .who:          String(localized: "content.commands.who")
@@ -54,12 +58,19 @@ enum CommandInfo: String, Identifiable {
     }
 
     static func all(isGeoPublic: Bool, isGeoDM: Bool) -> [CommandInfo] {
-        let baseCommands: [CommandInfo] = [.block, .unblock, .clear, .help, .hug, .message, .slap, .who]
+        var commands: [CommandInfo] = [.block, .unblock, .clear, .help, .hug, .message, .slap, .who]
+        // Cashu tokens are bearer instruments: in a public geohash any nearby
+        // stranger can redeem one, so don't *suggest* /pay there (the
+        // processor still allows it behind an explicit "public" confirm).
+        // Payments make sense in every DM and in mesh public.
+        if !isGeoPublic {
+            commands.append(.pay)
+        }
         // The processor rejects favorites in geohash contexts, so only
         // suggest them where they actually work: mesh.
         if isGeoPublic || isGeoDM {
-            return baseCommands
+            return commands
         }
-        return baseCommands + [.favorite, .unfavorite]
+        return commands + [.favorite, .unfavorite]
     }
 }