Add dark mode; gift amount unit toggle; multi-input gifts

- Dark mode: theme variables + a footer "Dark mode/Light mode" toggle,
  persisted and applied pre-paint via a small head script (defaults to the
  OS preference). Hardcoded surfaces moved to CSS variables.
- Gift amount: the unit label is now the clickable sats/BTC toggle, and the
  amount is parsed in the selected unit.
- Gifts can now span multiple coins: createGift selects several confirmed
  coins (first input SIGHASH_SINGLE to lock the change, the rest
  SIGHASH_NONE), so a gift larger than any single coin works. Claim/preview
  sum all inputs and size the fee by input count. Verified end-to-end.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

1 files changed, 2 insertions, 1 deletions

diff --git a/build.js b/build.js
index 52b29af..fbcd41f 100644
--- a/build.js
+++ b/build.js
@@ -141,9 +141,10 @@ export async function buildHtml({ minify = true, pwa = minify } = {}) {
 <head>
 <meta charset="utf-8">
 <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
-<meta name="color-scheme" content="light">
+<meta name="color-scheme" content="light dark">
 <title>Hal Wallet</title>
 <link rel="icon" href="${FAVICON}">
+<script>try{var t=localStorage.getItem('btc-wallet-theme');if(t!=='dark'&&t!=='light')t=matchMedia('(prefers-color-scheme:dark)').matches?'dark':'light';document.documentElement.dataset.theme=t;}catch(e){}</script>
 ${pwa ? PWA_HEAD : ''}<style>${css}</style>
 </head>
 <body>