Add ?string= param to T1 note-prompter

T1 previously picked the string only from localStorage (default low E).
Accept an optional ?string= URL param (1 = high e … 6 = low E) so wiki
deep-links can pin the string explicitly; invalid values fall back to the
stored/default string.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -102,7 +102,8 @@ Optional query parameters override the stored/default settings:
 
 | Param      | Applies to            | Example        |
 |------------|-----------------------|----------------|
-| `bpm`      | click-track drills    | `?bpm=66`      |
+| `bpm`      | click-track drills, T1 | `?bpm=66`     |
+| `string`   | T1 (1 = high e … 6 = low E) | `?string=6` |
 | `variant`  | drills with variants  | `?variant=2-3-2` |
 | `key`      | T2, T4                | `?key=D`       |
 | `root`     | T3, T5, T6            | `?root=A`      |