feat: gate registration behind 16 March 2026 19:00 opening date

- Add REGISTRATION_OPENS_AT const in lib/opening.ts as single source of truth
- Add useRegistrationOpen hook with live 1s countdown ticker
- Add CountdownBanner component (DD/HH/MM/SS) with canvas-confetti on open
- EventRegistrationForm shows countdown instead of form while closed
- Login page hides/disables signup while closed; login always available
- WatcherForm AccountModal guards signUp call as defence-in-depth

Closes #2

bun.lock

@@ -42,6 +42,7 @@
         "@tanstack/react-start": "^1.141.1",
         "@tanstack/router-plugin": "^1.141.1",
         "better-auth": "catalog:",
+        "canvas-confetti": "^1.9.4",
         "class-variance-authority": "^0.7.1",
         "clsx": "^2.1.1",
         "dotenv": "catalog:",
@@ -68,6 +69,7 @@
         "@tanstack/react-router-devtools": "^1.141.1",
         "@testing-library/dom": "^10.4.0",
         "@testing-library/react": "^16.2.0",
+        "@types/canvas-confetti": "^1.9.0",
         "@types/qrcode": "^1.5.6",
         "@types/react": "19.2.7",
         "@types/react-dom": "19.2.3",
@@ -909,6 +911,8 @@
 
     "@types/babel__traverse": ["@types/babel__traverse@7.28.0", "", { "dependencies": { "@babel/types": "^7.28.2" } }, "sha512-8PvcXf70gTDZBgt9ptxJ8elBeBjcLOAcOtoO/mPJjtji1+CdGbHgm77om1GrsPxsiE+uXIpNSK64UYaIwQXd4Q=="],
 
+    "@types/canvas-confetti": ["@types/canvas-confetti@1.9.0", "", {}, "sha512-aBGj/dULrimR1XDZLtG9JwxX1b4HPRF6CX9Yfwh3NvstZEm1ZL7RBnel4keCPSqs1ANRu1u2Aoz9R+VmtjYuTg=="],
+
     "@types/draco3d": ["@types/draco3d@1.4.10", "", {}, "sha512-AX22jp8Y7wwaBgAixaSvkoG4M/+PlAcm3Qs4OW8yT9DM4xUpWKeFhLueTAyZF39pviAdcDdeJoACapiAceqNcw=="],
 
     "@types/estree": ["@types/estree@1.0.8", "", {}, "sha512-dWHzHa2WqEXI/O1E9OjrocMTKJl2mSrEolh1Iomrv6U+JuNwaHXsXx9bLu5gG7BUWFIN0skIQJQ/L1rIex4X6w=="],
@@ -1027,6 +1031,8 @@
 
     "caniuse-lite": ["caniuse-lite@1.0.30001774", "", {}, "sha512-DDdwPGz99nmIEv216hKSgLD+D4ikHQHjBC/seF98N9CPqRX4M5mSxT9eTV6oyisnJcuzxtZy4n17yKKQYmYQOA=="],
 
+    "canvas-confetti": ["canvas-confetti@1.9.4", "", {}, "sha512-yxQbJkAVrFXWNbTUjPqjF7G+g6pDotOUHGbkZq2NELZUMDpiJ85rIEazVb8GTaAptNW2miJAXbs1BtioA251Pw=="],
+
     "chalk": ["chalk@4.1.2", "", { "dependencies": { "ansi-styles": "^4.1.0", "supports-color": "^7.1.0" } }, "sha512-oKnbhFyRIXpUuez8iBMmyEa4nbj4IOQyuhc/wy9kY7/WVPcwIO9VA668Pu8RkO7+0G76SLROeyw9CpQ061i4mA=="],
 
     "cheerio": ["cheerio@1.2.0", "", { "dependencies": { "cheerio-select": "^2.1.0", "dom-serializer": "^2.0.0", "domhandler": "^5.0.3", "domutils": "^3.2.2", "encoding-sniffer": "^0.2.1", "htmlparser2": "^10.1.0", "parse5": "^7.3.0", "parse5-htmlparser2-tree-adapter": "^7.1.0", "parse5-parser-stream": "^7.1.2", "undici": "^7.19.0", "whatwg-mimetype": "^4.0.0" } }, "sha512-WDrybc/gKFpTYQutKIK6UvfcuxijIZfMfXaYm8NMsPQxSYvf+13fXUJ4rztGGbJcBQ/GF55gvrZ0Bc0bj/mqvg=="],