Add share URL builders and embed format helpers for uploaded images.

Centralize clearnet/onion paths, delete links, and BBCode/Markdown/HTML output with unit tests and escape-html for safe HTML snippets.

frontend/package-lock.json

@@ -14,6 +14,7 @@
                 "altcha-lib": "^2.7.0",
                 "axios": "^1.20.0",
                 "dayjs": "^1.11.23",
+                "escape-html": "^1.0.3",
                 "hash-wasm": "^4.12.0",
                 "pinia": "^4.0.3",
                 "pretty-bytes": "^7.2.0",
@@ -22,6 +23,7 @@
                 "vue-router": "^4.6.4"
             },
             "devDependencies": {
+                "@types/escape-html": "^1.0.4",
                 "@types/node": "^22.10.7",
                 "@vitejs/plugin-vue": "^6.0.5",
                 "@vue/tsconfig": "^0.9.1",
@@ -1717,6 +1719,13 @@
             "dev": true,
             "license": "MIT"
         },
+        "node_modules/@types/escape-html": {
+            "version": "1.0.4",
+            "resolved": "https://registry.npmjs.org/@types/escape-html/-/escape-html-1.0.4.tgz",
+            "integrity": "sha512-qZ72SFTgUAZ5a7Tj6kf2SHLetiH5S6f8G5frB2SPQ3EyF02kxdyBFf4Tz4banE3xCgGnKgWLt//a6VuYHKYJTg==",
+            "dev": true,
+            "license": "MIT"
+        },
         "node_modules/@types/estree": {
             "version": "1.0.9",
             "resolved": "https://registry.npmjs.org/@types/estree/-/estree-1.0.9.tgz",
@@ -2454,6 +2463,12 @@
                 "@esbuild/win32-x64": "0.28.2"
             }
         },
+        "node_modules/escape-html": {
+            "version": "1.0.3",
+            "resolved": "https://registry.npmjs.org/escape-html/-/escape-html-1.0.3.tgz",
+            "integrity": "sha512-NiSupZ4OeuGwr68lGIeym/ksIZMJodUGOSCZ/FSnTxcrekbvqrgdUxlJOMpijaKZVjAJrWrGs/6Jy8OMuyj9ow==",
+            "license": "MIT"
+        },
         "node_modules/estree-walker": {
             "version": "2.0.2",
             "resolved": "https://registry.npmjs.org/estree-walker/-/estree-walker-2.0.2.tgz",