filter channel: lowercase #hashtag names before hashing

Hashtag channel names are [a-z0-9-], so fold operator input to lowercase
before deriving the key — #SelfTest now matches the real #selftest channel.
Safe since no valid hashtag name contains uppercase.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

docs/cli_commands.md

@@ -1146,7 +1146,7 @@ Repeater only. Lets a repeater decrypt channels it holds the key for, inspect th
 - `filter channel clear`
 
 **Parameters:**
-- `#name`: A hashtag channel, given by its name (e.g. `#selftest`). The key is derived the same way MeshCore clients derive it — the first 16 bytes of `SHA256("#name")` — so you don't need to paste a key. Only works for hashtag channels (named channels like `public` use a random key, not a name-derived one).
+- `#name`: A hashtag channel, given by its name (e.g. `#selftest`). The key is derived the same way MeshCore clients derive it — the first 16 bytes of `SHA256("#name")` — so you don't need to paste a key. Case-insensitive: the name is lowercased before hashing (hashtag names are `[a-z0-9-]`). Only works for hashtag channels (named channels like `public` use a random key, not a name-derived one).
 - `psk`: Channel pre-shared key, as either Base64 (the form MeshCore clients share, e.g. `izOH6cXN6mrJ5e26oRXNcg==`) or raw hex (`62be0e1267c401381f4ea6f44217d7a9`). Either way it must decode to 16 or 32 bytes. The literal `public` is a shortcut for the well-known public channel key.
 
 **Note:** Adding a channel only enables decryption/inspection of that channel; messages still forward normally unless they match a blocked keyword or sender. `filter channel remove <key>` drops a single channel — give it the same `#name`/PSK/`public` you added it with (it's matched by the resulting key, so any equivalent form works). `filter channel clear` removes all channel keys (the repeater stops decrypting and forwards everything blind again).

examples/simple_repeater/MyMesh.cpp

@@ -686,8 +686,16 @@ static bool decodeChannelKey(const char *psk, mesh::GroupChannel *ch) {
     memcpy(ch->secret, PUBLIC_CHANNEL_SECRET, sizeof(PUBLIC_CHANNEL_SECRET));
     len = sizeof(PUBLIC_CHANNEL_SECRET);
   } else if (psk[0] == '#') {   // hashtag channel: key = first 16 bytes of SHA256(name)
+    // hashtag names are [a-z0-9-], so lowercase the input to forgive operator case
+    char name[40];
+    int n = 0;
+    for (; psk[n] && n < (int)sizeof(name) - 1; n++) {
+      char c = psk[n];
+      name[n] = (c >= 'A' && c <= 'Z') ? c + 32 : c;
+    }
+    name[n] = 0;
     uint8_t full[32];
-    mesh::Utils::sha256(full, sizeof(full), (const uint8_t *)psk, strlen(psk));
+    mesh::Utils::sha256(full, sizeof(full), (const uint8_t *)name, n);
     memcpy(ch->secret, full, 16);
     len = 16;
   } else if (isHexKey(psk)) {